Black algae problem

[Danny56]

I have an above ground pool, 10,000 gallons with a vinyl liner and I think I have black algae or something living underneath the liner. The problem started when the pool was opened and it was completely green and dirty. So I figured I would start completely fresh by emptying the pool and scrubbing the bottom with bleach. After filling it back up again and adding all the chemicals, I noticed dark blue stains on the liner. Soon black spots/streams starting coming up and forming around the entire bottom of the pool (First picture). I did a triple shock and scrubbed it for about a week. Throughout the next few weeks I would shock it every few days and the stuff at the bottom would die and I'd vacuum it up. But after the cholrine goes back to the normal level (1-3ppm), the algae starts to form in the same dark stained spots on the liner. I kept the chlorine level high all throughout the next week and continued scrubbing but I am making no progress. Here I am about a month later and it still is coming back. Shocking will temporarily keep it away but it just isn't dying off. Could it be that this algae is underneath the liner itself? It comes back in the exact same spot where the liner has dark blue stains (You can see the stains better in the 2nd picture). No matter how hard I scrub or shock these dark blue spots/streak looking stains remain. Any ideas on what I can do?

 

[JohnT]

Welcome to TFP!

Chlorine won’t affect what’s under the liner, though it is possible for mold to grow under the liner.

Blue stains sounds like copper. Have you used copper algaecide?

 

[Danny56]

Thanks for the welcome,

I did try a copper based algaecide about 2 weeks ago but it hasn't made much of a difference. I find it strange that the algae continues to popup in the same stained spots after all the shocking. Sometimes the algae looks more dark grayish with a hint of green on the outside of it than just black, but it brushes away easily. Maybe it might be some type of mold instead that keeps growing back?

 

[Fast7]

I think you never completely eradicated your algae bloom you had when pool was opened.
"Shocking" is not enough to kill algae. We use process called SLAM.
We can guide you thru but in order to successfully perform SLAM you need to be able to test your water frequently.
There are only 2 test kits we recommend. Check Test Kits Compared.

 

[Danny56]

I use basic testing strips and would really not like to purchase an expensive test kit. According to the SLAM process, wouldn't I be continually adding shock to keep the chlorine level high? After a triple shock in my 10,000 gallon pool it takes 3 days for the chlorine to return to normal levels, so would adding an additional bag of shock each day after the initial triple shock be enough to keep the chlorine level high enough to kill it?

 

[Fast7]

I understand completely that test kit might seem like a waste of money if you can get test strips for a fraction of the cost.
However there is really not a way around it, because test strips aren't that accurate, but more important can't test past 10 ppm FC.
Take a look at this chart Chlorine / CYA Chart. Depends on your stabilizer level (CYA) you need to reach and maintain specific FC level.
All SLAM levels require at least 12 FC (we recommend minium 30 CYA)
It is simply impossible with test strips. The only test that can read FC up to 50 ppm is FAS-DPD type.

I guess you could have someone in your area, neighbor, friend, family member or as last resort - pool store, test your pool water for CYA.
Then you can just get chlorine (FAS-DPD) test and use it for SLAM.

Oh, and we don't use any dry or powder shocks because it will either keep increasing your CYA (stabilizer) or CH (Calcium Hardness) to a point where you would need to drain and refill your pool.
Liquid chlorine, aka bleach, is the only thing we use to sanitize our pools.

 

[critter783]

The test kit is expensive up front, but it pays for itself in chemical savings once you have the water chemistry under control. With a FAS-DPD chlorine test, you can be very precise in how much chlorine your pool consumes daily, and replenish accordingly. Also, if you have visible spots of algae growing in your pool, then there's definitely algae suspended in the water that you can't see, and without a proper test kit, you can't know for certain when the microscopic stuff is finally dead.

 

[Tpopz]

I use basic testing strips and would really not like to purchase an expensive test kit.

We’ve all been there.

Accurate testing + TFP resources = more time enjoying your pool........It’s that simple.

 

[Danny56]

Thanks for all of your replies. I went to my local pool store and they tested my water. They said everything was perfectly fine. They recommended that I raise the chlorine the pool really high and scrub the algae away. I did some research online and found out that fungus or bacteria could grow underneath a vinyl liner. My liner is probably over 8 years old and it's badly faded. A month ago I drained the entire pool and scrubbed the floor with bleach. Just 2 days after refilling it this black stuff reappeared in the same spots. At this point I'm convinced there is some type of fungus underneath my liner. My chlorine has been high straight for weeks now and if anything the black stuff is getting worse. Particularly after it rains. I'm probably going to put off a new liner until next year, but is it safe to swim with this stuff now? I am dying to get in the pool but I've been afraid to do so with the algae or fungus I have. I attached an updated picture of it to this post.

 

[Jezza]

As mentioned earlier and until you get one of the recommended test kits it’s likely your going to continue to go around in circles.

We need reliable test results from one of these to be able to advise you what your next steps should be. The pool stores testing and advice is usually a poor substitute and can’t be relied upon.

 

[mknauss]

But after the cholrine goes back to the normal level (1-3ppm)

The above is the issue. You are not following the FC/CYA Levels using a proper test kit after completing the SLAM Process to its conclusion.
Without a proper test kit, you will not get off this hamster wheel the Pool Store has you on.

Good luck.

 

[jmikeb]

danny-
did you ask your pool store how “perfectly fine” water can have algae ? i think that’s very telling.