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Unidentified algae in in-ground pool


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Hi! We had an algae/bacteria develop in our pool that 2 different pool stores were unable to identify (multiple people looking at my pictures, etc). From my google searches, it does not look like pink slime, green algae or black mold. It looked more like mucus or the insides of a snail. I have attached pictures. I treated it as if it was pink slime & followed instructions from pool store (brushed sides of pool, ladders, vacuumed multiple times to waste, backwashed & shocked 2 different times with all tools in pool when shocked). Pool is clear now. No one has been in the pool yet (too cold) except for a hired diver to check for liner leak (could be the source). Hoping it doesn’t come back but my question is: does anyone know what this is?!? Would like to know so if it comes back we can treat it appropriately. Thanks! 

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  • 2 weeks later...

It looks like pink slime or a similar bacterial biofilm to me. Are you using chlorine or biguinide/peroxide? It is more common with biguinide/peroxide sanitation but can occur in a chlorine pool if you are not maintaining proper free chlorine levels or if your pool is overstabilized (Cyanuric acid too high for the FC level being maintained). Posting a full set of test results (from the time the problem occured) would be helpful in identifying it but even a current set of test results might be illuminating if you are using chlorine.

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Thank you for your reply & information. We have a salt system and I have attached a picture of water test results from the day I started noticing the problem. Another note: there seems to be a rust color developing around the bottoms of the ladders and around the light that seems to be getting worse if that gives you any information. Thank you!image.thumb.jpg.94910e181fa1802e83d230712fcf0c0a.jpg

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What make and model of salt system?

Your water is WAY out of balance. There is practically NO chlorine in the pool so either the salt system is not working, is not set right, or there are 'nasties' in the water that are consuming the chlorine (but if this were true and everything was working you would have very little free chlorine and very high combined chlorine. I suspect that you have been in a very low chlorine/too low cyanuric acid  situation for a while and that allowed the slime to grow.

I also notice that your Cyanuric acid is way too low. Just about every salt system on the market recommend CYA in the 50 to 100 ppm range, depending on the make and model. For example, all the Hayward/Goldline and AutoPilot models recommend CYA between 60 to 80 ppm with the higher end preferred.

You also did not list your salt level. If it is too low then the unit will not generate chlorine and most units will shut off if it is too high also.

If you have a plaster surface pool then your calcium saturation index is WAY out and can cause damage to the pool surface. IF you have fiberglass or vinyl then it's not that important. However, your TA (alkalinity) is too high for good pH control with a SWCG and should be around 60 or 70 ppm.

Don't worry about phosphate and DO NOT LET THEM SELL YOU A PHOSPHATE REMOVER. That is NOT what is causing the problem causing the low chlorine.

54 minutes ago, KristineM said:

there seems to be a rust color developing around the bottoms of the ladders and around the light that seems to be getting worse

You have iron in the water which could be a cause or your improperly set up salt system and unbalanced water, combined with metal ladder, light ring, or even screws used to secure them could be actually rusting because they are not 'salt safe" (there are ones desingned for use in salt pools, btw). This could be the source of the iron in your pool water, btw.

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These are the results from water testing over the weekend. We have a Pool Pilot system which normally does a good job. Our pool has a vinyl liner. We shocked the pool last night and the output this morning is 33% (regulated by the pool pilot). Thank you so much for all of the information-I’ll take in another water sample and get the cyanuric acid level taken care of. I’ll treat the algae as if it was pink slime if it comes back (very possible😞). Do think algeacide will help if it is a bacteria? Or just shock (pool store recommends liquid shock but we can also get granular shock)? Let me know if you have any other suggestions. I appreciate your help.

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How is the pool store testing? Liquid reagents read in a meter of some sort? Strips?

It's very strange that the FC and Cc are the same in both tests you posted but if they are correct your system is NOT producing chlorine. What is your salt level? FWIW, I use to sell Pool Pilots and am very familiar with them. Calcium is fine for a vinyl pool, btw but your TA is a bit high for best pH stability although a pH of 7.8 is fine.

Best thing to shock your pool is either liquid chlorine or plain, unscented, unthickened chlorine laundry bleach such as Clorox or a store brand  (they are all sodium hypochlorite and only differ in strength and therefor how much is needed to raise the pool to a specific FC level. This is also what your Salt system is producing and adding to the water so it's the most compatible form of chlorine. However, since your CYA is so low right now you might want to consider shocking with dichlor, which will add 9 ppm CYA for every 10 ppm FC added and the bonus is that it is very fast dissolving so the CYA is available immediately as opposed to adding plain CYA which can take several days to fully dissolve.

My final suggestion is to purchase a Taylor K-2006 test kit and start testing your own water. For testing your salt levels I would recommend the Hach or AquaChek salt test strips (only strips I recommend using are these and the LaMotte borate test strips if you decide to add a borate product to your pool, which is an excellent thing to do for a salt pool for several reasons that I won't go into right now since I don't have the time. )

You can find the Taylor test kit online at Amazon and many online pool supply retailers. It is probably the MOST important piece of pool equipment you can own and worth every penny. Do not get the K-2005 kit, You want the K-2006. Here is a link to the Taylor Technologies website that had videos on the use of the kit:

https://www.taylortechnologies.com/en/page/231/k-2006-complete-kit-with-fas-dpd

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Salt level is good but the fact that you have no chlorine in the pool  makes me think that your cell might be bad. They only last for about 5 years so you might want to get it checked. If the biofilm was consuming the chlorine you would test little to none FC but the CC would be high as would the total chlorine. The other possibility is that your chlorine level is very high and the chlorine tests are bleaching out and reading low. This is a problem with DPD testing which is why I recommended the Taylor K-2006 which uses the FAS-DPD testing method which is easier and does not have the bleachout problem. However, this would not explain the fact that biofilm is growing in your water. Does your pool store test by using a disc and then reading it in a machine by any chance?

 

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The pool store reads it using a meter of some kind. I’ll get that test kit on amazon-thanks for the recommendation. I’m going tomorrow to get the water tested so I’ll ask them how exactly they test. We purchased & installed a new salt cell 2 summers ago. Is it possible we need a new one already? 

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