What kind of algae is this?

We have been dealing with some kind of staining since we opened the pool this spring.

In ten years, this is the first time we have had any problem like this. By the time I realized it was some kind of algae, it had spread all over the deep end floor and a lot of the wall areas. The water was pretty much crystal blue the whole time.

Since finding the forum, I have discontinue tabs and started using the BBB method.

I have had my chlorine up over 10 ppm for about one week and now when I brush the pool surface the bristles of the brush are covered in a brownish sticky tar like residue and the pool is finally starting to slowly clear up. I have also been adding super algaecide every day also.

Before getting the chlorine level up when I brushed I never got an residue on the brush.

What kind of algae acts like this and do you think I have finally turned the corner on this?



16 x 32 inground 20,000 gallon
PH 7.2
TA 160
FC 11.5

We really need some more information to be able to help. Specifically, we need to know your CYA (stabilizer) level and your CC (combined chlorine) level. I have a feeling if you have been using trichlor tabs for a long time, your CYA level is gonna be really high. Is this a vinyl pool?

Stop adding the super algaecide. Algaecides are a pretty good preventative, but don't do much after you already have an algae bloom.

I'm not sure what the brownish sticky stuff is. Repost with the needed numbers taken with a drops based kit and also tell us exactly what all you have added to the pool --- meaning ingredients. Someone here can take a look and try and help.

BTW -- Welcome to the forum!

EDIT -- Also, tell us what type and size your pump/filter is.

I agree with Watermom. I'm guessing your CYA is over 100 and you probably should be keeping your FC at 25--but do NOT move it there until we know the test numbers.

In the meantime, increase your FC to 15ppm and do the following:
1) Continue to brush it everyday.
2) Vacuum to waste everyday--you don't want that stuff in your filter and the more you can physically get out the less you have to chemically deal with.
3) Stop using algaecides. To refine what 'Mom said, there is ONE good algaecide, Polyquat 60%, that's mainly good to prevent algae, not kill it. The other algaecides are going to cause you more problems than you can imagine. In fact, if you've been using an ammonia-based one, it may be helping create the sludge. If so, the good news is chlorine should break that down albeit not as quickly as you'd like.

Here are the numbers
FC = 5.6
CC = 0
PH = 7.2
TA = 160
CYA = 110 ish

This is a vinyl liner pool with a TA60 Pac Fab sand filter system. The sand is about two years old in the filter.
The liner was installed last July.
I have been adding 182 oz. of bleach each evening (6% sodium hypochlorite), HTH brand Super algae guard which does have ammonium in it. This has been my daily program for about 10 days.

I used to use trichorl 3" tabs before switching to bleach about mid June.

Once I figured out it was some kind of algae, the pool store here gave me a bottle of Banish and that did not even touch it. After that I used Yellow Out. That seemed to lighten the algae a little but after a couple of days the staining came back. I then tried the Yellow Out a second time. I also threw in a bottle Algaecide 60 from IN THE SWIM.
Probably have been using good much algaecide.

I did drop a puck on the surface and the algae burned off under and around it. But in a day or two you could see the algae covering the area again.

Before I started adding the algaecide, whenever I brushed nothing happened. You could brush and brush and there was no noticeable change and didn't look like there was anything to vaccum up but you could daily see the algae staining spreading.

Any help is appreciated. Thanks.

With a CYA over 100, your shock level is going to be 25ppm. Test at least 2 and 3x or more per day is even better and each time, raise your chlorine level back up to 25ppm with bleach. The key to killing algae is to sustain the high cl reading and not let it yo-yo up and down. Do this until you can go from sundown to sunup without losing more than 1ppm of chlorine. At this point, you can let the cl level drift back down but with that CYA reading, you will have to keep your chlorine between 8-15 ALL the time or your algae problem will come back. Also, brush the pool daily and run the pump 24/7 while you are trying to clear this pool. BTW -- In a 20,000 gallon pool, each 3-quart jug of 6% bleach will raise your cl by just a little over 2ppm.

No more trichlor tabs nor dichlor powder shock for your pool as they will continue to cause your CYA level to rise. It is already WAY high. In fact, you might want to consider doing a partial drain and refill and drain about 1/2 to 2/3 of the water to lower the CYA to a much more manageable level. Do NOT drain the entire pool however.

Sand doesn't need to be changed. Mine is something like 10 years old and doing just fine.

No more algaecide. At this point, just lots of bleach. Also, keep an eye on your pH and make sure it doesn't drop any lower. Anything below 7.0 is acidic and can damage your pool. Watch the pressure on your filter. When it rises 8-10 psi over your clean filter pressure, backwash.

Good luck. Keep us posted how things are going.

Watermom's given you the prescription--I just wanted to add that the Yellow Out, Banish, and all the algaecide you added have created a really big chlorine demand by themselves, and that combined with the high CYA is why your chlorine was not being at all effective against the algae. Algaecides are much better at preventing algae than actually killing an active bloom, but even then we only recommend Polyquat 60. The othe algaecides can cause all sorts of problems including foaming, copper staining, and breakdown into ammonia, which creates an even bigger chlorine demand.

So...like Watermom said, don't put anything else in there but chlorine--no trichlor or dichlor--and get that chlorine up to 25 ppm and keep it there until the algae is dead and you stop losing chlorine overnight. Keep the filter running, and keep an eye on the pressure--backwash it as necessary. It will clear up--but again, the key to keeping it clear is to never let your chlorine drop below 8 ppm. (or even better, drain/refill part of the water to get that CYA down)

Janet

Once I get the CYA down to 40 to 50, would I still need to get the FC up to 25ppm to kill off the algae?

No. With a CYA of 40 or 50, it would only take about 15ppm of chlorine to kill algae.