How To Get Rid Of Dead Algae From Bottom Of Pool?

Hi John.....I hope you can give me some pointers as to how to get rid of all the dead algae on the bottom of the pool.

We've added floc to clump and sink the dead algae (which it did) but now find it impossible to hoover it up, as every time we attach the hoover to try and hoover it, the return jet stirs up the water so much that the algae is disturbed and turns the water a cloudy blue.

The chlorine and ph levels are fine. Our pool is 10m x 5m.

Hope you can help....thanks in anticipation. Shona.

Hi Paul, I can totally understand your position, 17 years was quite away back and generally pools were owned by people who had the kind of budget to allow for it.

Construction methods have changed considerably from the old labour intensive block and skilled bricky days. May I ask what the walls are constructed from on your pool? looking towards the difference in construction method used for your year of Desjoyaux and what your other more expensive construction you were quoted for.

I know I do go on not only about Desy but Magiline and Waterair too, in fact any pool where the filtration is a unit construction with the filter and return built in as they are not efficient, I am not saying not effective just not efficient by todays standards. As I said to Simon Othern, it is precisely because of the hydraulic inefficiency of these mono block types that I knew I could develop a far more efficient pool filtration system, It was not easy as pools have never been efficient hardly any of the components work effectively if you lower the power as I have done so more attention to how the water actually moves, copying nature and computerised fluid dynamics to examine the results have all been costly. It is also why the monoblock filtration units have bigger more powerful and therefore more electricity to overcome the shortcomings I have found but I am smarter than these companies who's marketing depts say "pattented" that just means a different way, an original not that it is any better.

I am working towards reasonably priced conversions for Desy, Magiline, Waterair and other mono block units including the Crystal pools from Piscine Plus. With financial break even in 2-3 seasons.

This year I am winding down the power on my pool to see at what point the water clarity gets poorer. I am not using the human eye as that is good enough, I am using a lab grade turbidity meter because only then can we quantify the results rather than anecdotal gin clear etc which just shows how poor the human eye is because the water when it clear enough having had contaminants removed is so much easier to look after with less chlorine so less chlorine byproducts.

To end, it's really to try and prevent people believing the sales patter form these pool companies, I have sat through the dealer presentation for the 3 I mentioned earlier and I can assure you they don't talk much about the pools it's all about the income they can make.

I would rather show these companies for what they are in the modern market place, what happened years ago before we got concerned over Co2 is the reason we must now sit up and listen, the old excess must be reduced where possible to ensure the continuation of our marine life 2050 is not far away to see species of fish dying in the oceans because we have every electrical item under the sun and are producing way more co2 than the earth and oceans can handle.

John, the trouble you go to and the length/detail in your posts is very much appreciated by all of us out there with pool issues.

Having installed a DJ pool (Desjoyeaux) 17 years ago and for most of that time it has served us well, I am naturally a little defensive about it's virtues. One of these is initial installation costs. In 1998 I was quoted a difference of £12K to £15k between a DJ and a conventional pool. Going forward from that point I reckon on being still well in pocket even with higher electricity and maintenance costs.

Your advice has been great and helped immensely with recent algae and dead algae issues, but what us DJ owners must do is manage what we've got going forward. Conversion would probably (?) be very expensive, so more attention to things such as replacing the filter bags more often, utilising a proper water testing kit, running the filter system for sufficient hours every day etc. etc. is my way forward.

Some may say that 'Hindsight is a wonderful thing!' but we are living the dream with our house in the Dordogne and it's swimming pool.

Thanks again John from an avid reader of your posts.


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Hi Simon,

Not sure why you mention your salt and pH doser, I have no trouble with that system, long may it keep working.

Good that the filter has lasted so long no issues with that and yes because there is one quite powerful pump (consuming a fair amount of electricity) you are getting some flow. Now if we take the logic of moving water, it makes more sense to move it from one side to another rather than just from one end back to the same end which by definition cannot work as well. This is simply because it is actually moving twice a far. It is often the case that pool companies set the water to rotate in a circle around the pool, this will create dead spots in all four corners but worse than that you get a dead spot in the middle of the pool which is where the leaves etc make it to and then sink. No problem just bring in you pressure side robot to clean it more capital outlay and more electricity to run that too.

So now I am not having a go at you, I am having ago at the monoblock filtration setup that many companies use and most of the pool industry who set up moving water around a pool. Who decided that was best? why do so many pool companies copy each other?

I can only surmise because R&D costs money, so they stick with what they know from the last century and they don't really care as they pick up additional sales for robots etc.

Different forms of the monoblock filtration systems are around some using 1200 watt/H pumps, some 1800 watt/H pumps and some on larger pools using 2x 1200 watt/H pumps. All because it's easier for them to install as it's pre built in a factory and the on site block layers cannot get it wrong but this is not an efficient way for the owner to have their pool.

I and some of my fellow pool colleagues world wide looked at the problem from a fresh new perspective and using computational fluid dynamics software looked carefully at the flow around the pool basin on a few common shaped pools and from this we calculated the very best way to do it.

My specialist field is the hydraulic circuit from my days as a hydraulic and pneumatic engineer. From this I have been able to re engineer the flow system to run on a tiny amount of electricity but also produce far better results. This has meant I was able to sell my pool cleaning robot, it's not required any more. The pool runs on a variable speed pump and during swim times consumes only 69 watts/H outside of the swim times it runs on 35 watts/H.

A larger pool we converted the other year was using a 2,200 watt/H pump, it is on it's second season and runs on 120 watts/H

When most people manually vacuum their pools a small dust/dirt cloud appears in front of the brush/vac head so they move slowly to not disturb this and try to vacuum it up. I don't have that dust cloud, the water is far cleaner because of it and because of that there is less work for the chlorine to do so that lasts longer.

None of what I do is pseudo science, I have the empirical data to back up everything I do, I have traveled many thousands of miles and spent a fair amount of money to produce the most efficient swimming pool filtration and flow system available, the work is continuing as I have a new filter design I am working.

This work could have more far reaching consequences as providing safe clean drinking water in the 3rd world is a major challenge because electricity is not widely available and banks of solar panels are expensive and require someone to guard them. Working with other water professionals my low energy solutions could bring safe clean drinking water to these people.

If you have any reason to believe that what I do is pseudo science, I would ask you to please be as specific as possible and I will try to answer any questions you have.

I was hoping that you would ask more about the sand filter you are having issue with.

we have a salt and auto Ph system on both which have never given any trouble, and our big filter cartridge has lasted 9 years, there is excellent flow around the rectangular pool, and the flow rate is very good and circulates around the pool completely as long as the direction hear is angled correctly, the polaris robot that sweeps the bottom though outward flow and a bag on the robot body also does a great job and will clear any leaves etc . I was just saying it is not good practice to slag off companies, especially if you group them together ........comment about single companies one at a time is fine.

So please dont confuse people with your pseudo science as it does not help !

Very glad to hear that Shona, I wondered how you were getting on. I wasn't far away from you the other week, just south of le Blanc at Badecon le pin. I see now you had lots going on with Stuart, hope that went ok too.
As I said a post or two ago, keep your chlorine a little higher at this time as it's a seasonal algae bloom time. not been near a Desy pool for a while so still not measured the bags but it's on the card as I have to prevent a poor owner from being conned into €500 for his close up at the end of the season.

I meant to add a comment on here a couple of weeks ago, but due to my husband being in hospital (long story, but it involves a hip replacement) it really wasn't my number one priority.

Anyway....I'd like to let everyone (especially John) who added some input into solving my problem re the dead algae know that we finally have a CLEAR POOL.....woo hoo! It took a long time, and lots of letting dead algae float to bottom of pool, and lots of hoovering , and lots of changing socks, and various other things that were suggested, but finally it's clear. The relief is unimaginable. When people are paying (we have gites) to come on holiday expecting a pool to not only be blue, but clear at the same time you really want to give them what they're paying for.

Thank you all again, and here's hoping we don't have a re-occurrence next year when get ready for season 2015.

I tend to agrre with John about Magiline pools, they are fine when they work but the overcomplicated filtration and pipework system makes fixing them when they malfunction a nightmare. We've fixed leaks on lots of pools and the Magiline pools are the hardest to do. Personally, I would never have one

Dear Simon thank you for your contribution, you are entitled to post what you believe is the best way you see to deal with issues Just as I am, the difference being I understand the science behind swimming pools and the chemistry so no mis information from me.

Now your first point, "the only way to get rid of dead algae"? there is really no other? When people are under pressure to get the pool clear, often with guests arriving they need to have methods which may not be 100% effective but ones which are better than 50% and quick. That is why allowing dead algae to settle and vac to waste is used and used by a lot of people. Sure if you have time then filtering it out is ok providing the filtration is fine enough to catch it so it doesn't just get returned to the pool basin.

"When you have a green pool, put in a bucket of choc" Really, and that isn't mis information? One of the most common reasons for a pool going green is a high level of cyanuric acid stabiliser (CYA) which comes from packaged products like Chlor lent, Chlor multiactions & chlor choc. The only packaged product that doesn't contain CYA is calcium hypochlorite as sold by HTH commonly in France or liquid chlorine (eau de javel) therefore adding a "bucket of choc" (your post didn't describe which type) can make the situation even worse. Choc is a process and NOT a product, choccing a pool is raising the free chlorine level to a point where full oxidisation of everything living in the pool takes place AND holding that level at a sufficiently high level for long enough to ensure all the algae is killed and all disinfection byproducts are oxidised out of the pool. All choc pastilles/granules are the same as a basic galett but smaller so they dissolve quicker, there is no magic, same product but liquid chlorine works even faster as it mixes quicker because no time is wasted dissolving it.

As to slagging off Magiline, I am very grateful to Magiline, Desjoyaux and Waterair, Yes of course they work and providing you don't get into trouble water wise you won't notice the difference. The difference is when there is an issue they take a lot more work to get them back to clean and clear. Take your Magiline system, the brochure would tell your it circulates 50m3 per hour by it's wonderful system. Well it can't, If you look at a swim jet counter current device, these flow 50-60m3 per hour (Badu swim jet) this requires a pump of 3-4 Hp and no filtration in the way. your much smaller pump cannot push that much water in that amount of time due to dynamic headloss and draw it through a filter element, it's impossible due to the laws of physics.

The other points with these systems are that they have a single return nozzle placed very close to the skimmer, so water is returned and doesn't flow up to the far end of the pool and circulate the chlorine to all areas. The water moves around in the skimmer area and is drawn back in leaving the majority of the pool with very little flow. Eventually the water and chlorine will get there but the flow is very poor when compared to a conventional system. This can be tested with some food colouring.

Maintaining a slightly higher chlorine level does help in these pools as it provides more of a buffer against a drop in chlorine in corners etc. Depending on the size and shape of the pool the system can also work marginally better in a curved/hexagonal pool than say the 12m x 5m Desjoyaux I was first introduced to many years ago.

Now I am very grateful to these companies as I said, they help me to earn an income but they also made me question if these things can actually work with such poor filtration (Magilines filtration is better than Desy's) and water flow which again is so poor but they do that at the expense of having larger usually bespoke pumps which cost more to run in electricity are more stressed so likely to fail sooner, what could I do with my knowledge of hydraulics to provide a better flow and far less energy, as the Magiline, Desy and Waterair demonstrate very little flow can still work if all the other parameters are good. That has meant I have developed the most efficient, ultra low cost to run pool flow and filtration setup which only uses 10-15% of the electricity a conventional pool uses saving thousands of euros over a 10y period. More than that the water quality is far better, the chemical usage drops and there is less manual maintenance to do. all thanks to some of the worst designed pools in France.

Back to your sand filter issue Simon, not all sand is made equal, some sand is better than others, I was working on a pool near me a couple of weeks back and the pool is having trouble clearing, I have had a good look and cleaned the sand but the sand in the filter is too course so dirt is just passing through. I should have been back to that by now (sorry Andrew) and replaced the sand with AFM glass. Now I don't know the details of the setup you are struggling with but not all sand filters are created equal either, some have very poorly made laterals which in the case of one pool only had about half of the slots molded cleanly so water flow was too fierce through the remaining ones and channeling of the sand occurred and poor backwash performance meant too much muck was retained in the filter which then meant more chlorine was being consumed, in effect it was a biological filter not a pool filter.

If you post more on the sand filter system giving you trouble maybe we can take a look at it?

In closing, I will just add that we seem to get two algae blooms each year and the next one seems to arrive early August, I have already been notified of two pools going green, so just as a warning to keep your chlorine levels up a bit over the next few weeks.

hi, a lot of misinformation in this thread, the only way to get rid of the dead alge is to sweep it into the water and let you filter take it out ...simple, same as when you have a green pool, put in a bucket of choc, sweep every hour, clean your filter every 2 hours if you can, leave the pump on for 24 to 48 hrs ...job done !!!! and please dont' slag off magaline, we have a beautiful pool built by them 9 years ago and its is crystal clear and working fine, we also have a new pool with a sand filter that is still struggling to stay clear !!!!!!!

Hi Shona, Glad you are getting somewhere, I know it's not easy and my post seems rather harsh on people but I am for the facts not the chat, although over a cuppa...... You will win through, it takes time and a bit more chlorine does help because your single return jet doesn't get a really good mix of the chemicals over the whole pool. Using eau de javel from a Brico rather than galetts will also help as too many galetts build up the stabiliser level too much and that causes more issues. 750ml would give you around 1ppm and running your pool at around 2-3ppm always, will benefit you. Can't be more precise without accurate water test results but it's a good place for you to start.

50€ a bag! I would bet my..........on it. Back in France next week so I will measure the bags, maybe an idea if you do the same as the unit's did change a bit over time so maybe the bags did too.

Hi John

We've now resorted to good old hoovering the pool every morning to pick up the debris and then running the pump as per normal during the day. We've tried leaving the socks uncleaned for longer than normal in the hope that the more clogged up they get, the more debris is going to get trapped. This works up to a point, but then the pump starts to struggle as there's not enough water getting through.

The water is getting clearer, but nowhere near as clear as it should be......maybe by the end of the summer we'll have cured the problem!

Thanks for all your (and everyone else's) support and replies.

By the way , have you come across any other supplier of finer, cheaper Desy-like bags.....i.e. less than 50€ a pop?

Ok back from the no internet place and sat down to see how Shona/Stuart got on.

If you are unfortunate enough to own a Desjoyaux, Magiline or Waterair, come to think of it any pool with the single monoblock filtration system please make this clear in your opening post. I had my suspicions when Shona mentioned one return as no self respecting pool builder would ever use a single return.

Yes flocculent with the regular bag filter is pretty pointless as it's more of a strainer than a filter in the true sense of the word. Desy do have a finer filter bag available which could help in that situation. I will measure the bags when I next attend to a Desy pool as I am sure the size will be available elsewhere for a lot less. I don't really want to go round servicing Desy pools would rather re configure them to a proper filtration system.

It would be no mean feat to re engineer a monoblock like Desjoyaux to a sand filter as they have been made that way so simpleton installers require less actual training and average builders don't have to think about what they are doing. Does it sound like I hate Desjoyaux, Magiline and Waterair? well that's because I do, they sell poor systems to un suspecting people who struggle with the pool when a normal system would have worked so much better and on half the electricity.

On to some of the replies:

Véronique, you follow the usual french path and add peroxide, the problem is peroxide is a really strong oxidiser but a poor bactericide so whilst it may kill some algae by oxidisation only it also is a stronger oxidiser than chlorine so it burns the valuable chlorine out of the pool as well and as it hangs around for a few weeks your pool can get into a worse state because you can't keep chlorine in it. This is usually sold by French pool shops as a solution because it earns lots of money because peroxide is expensive. Chlorine works faster, more effectively and is a fraction of the cost.

Flocculent is a subject on it's own but water treatment companies use it (in the correct way) to supply your tap water which is in the main free of all snot.

John Bowman, please read the preceding posts before posting, there is already a description of how flocculent should be used and in a pool it's almost a waste of money if done the way they say on the packet to use it. There isn't a sand filter. As for "Best to ask your Desjoyaux dealer" You are joking, the only thing a Desjoyaux dealer knows is the quickest route from your pool to his cash register!

Ok Shona, yes you are a bit stuck but Stuart sounds enterprising enough to use a work around with some success. Try the finer bags and dream of a better system.

What's wrong with the system, it takes ages to clear a pool, ok if you get it clear and keep it that way you may not notice how poor it is but you sure do when it plays up! The biggest issue with these monoblock units is the pumps are larger and more expensive and often bespoke to the pool so when they go wrong you pay a lot for replacement. The way it's setup is poor. The filters are on the pump intake not on the pump out flow as with a conventional setup. It is massively inefficient to do this, try it for yourselves, try sucking out the candles compared to blowing out the candles on a cake to see what I mean. Air and water don't like to be sucked they like to be pushed and by pushing you can use a smaller pump to do the same job which in turn saves about half of the electricity/money of say a Desy pool.

Today we attached an extra hose on to our return valve and diverted the water out into the garden so that the water wasn't being disturbed as we hoovered. This worked up to a point, but the water going out the pool was greater than that being replaced by a hose from our well, and the water level dropped quite quickly.

We've been cleaning it using the skimmers only this afternoon and cleaning the socks regularly. The water's looking clearer, but nothing like it should be...nevertheless I had my first swim in it this evening (24 degs). Lovely!

I never use floculant in my pool because I'm unconvinced that all the bits of snot will be got rid of: I use concentrated peroxide to kill the algae & then filter (or use my pump method if need be, in extreme situations) my pool is almost always lovely in spite of the no-floculant rule.

Bonjour Shona

Put the 'hoover' away!

Go to your pool shop and buy floculant tablets. These you put in the pre-filter basked (not skimmers) which should be just before your pump. These dissolve and will cause any particles, dead algae or dirt, passing through the pre-filter to stick in the sand of the filter.

Run pump for 24 hours then backwash and rinse. Repeat if necessary with more tabs.

If you have a Dejoyeaux system, you will need to hose down the filter probable after he first 15 to 30 minutes and then at half-hourly intervals for several hours. Best to ask your Dejoyeaux agent about this.

Bonne chance.

Sorry I thought the OP had a proper filter set up, I have a standard sand filter which has been in place now for seven years and the running costs are nil. No new filters to buy no flocculant, crystal clear water and maintenance ? Well an annual back flush and rinse, about 20 minutes. Go for it!!!

Another thing you can do is switch off the pool pump and connect your hoover hose to an external pump (pompe cave type) and send the dead algae off into a bit of your garden. Or if you can't connect it, then you attach your pompe cave to a pole and use it as a hoover, again sending the algae away into the bushes - fiddly but it does work very well. Then top up the water if need be & put your pool filtering back on.

We too had a lot of algae in our pool (magiline, v similar to desjoyaux). We have worked hard to clear the bottom, using the robot and by deliberately disturbing the clumps so that they go through the skimmer and are picked up by the socks. When we started we were rinsing the robot bag and the socks every hour and hosing the filter cartridges every four hours. It’s taken a bit of graft but the pool is now crystal clear.

John, Adding to what Shona said. It seems to be that the particle clumps cannot be filtered by the socks and just pass through. You can actually see a cloud coming out of the return jet. Hence we need to divert the return water to waste. It is a standard Desjoyaux pool with double basket & sock filters. Now considering installing a sand filter.