Lowering CYA

[jrsdws]

So I closed last year after having my first swimming season of algae troubles with my 27' above ground pool. I had multiple algae blooms through the summer.

After finding this sight I bought a TF-100 test kit.

My CYA was way high....always over 100. It was taking me tons of shock to get to shock level and keep it there.

Upon closing, the water looked pretty good and I drained about 1/3 of the water.

I now have a swampy green pool that has taken on alot of spring rain water and my CYA is between 90 and 95.

Should I drain down to about 1/3 water remaining and then refill to lower CYA?

I am going total BBB method this year.

[PoolDoc]

If you can easily drain, that might be the best thing to do.

Keep in mind that if your CYA was REALLY high (>150ppm) you may have a lot of ammonia in the pool. There's no easy way to tell, at present, but if you do it will *still* take enormous amounts of chlorine to clean up.

Also, if you drain 1/3, your CYA will only go from 90 to 60 -- still quite high if you plan to use stabilized chlorine.

Under the circumstances, you might want to add a 10 gallon dose of bleach in the late evening, and then test an hour later for both FC and TC. Test again the following AM within 2 hours of sunrise. Then post the results. Those results will give us a much better idea of what your situation is.

Ben

[jrsdws]

I haven't filled the pool up yet to start the clean-up process so I have no circulation unless I hook up another pump and just circulate it back into the pool? This won't move as much water as fast as the pool pump, but I suppose it would work?

CYA was likely always around 100-110. Pool is in full sunlight.

Draining to about 1/3 left in pool is not a big problem if that is the best thing to do. I can drain down to 1/3 and then refill...get it all running and add 10 gallons of bleach. It will all take me a few days, of course.

Whatever you think is best....I'll do it.

[chem geek]

If bacteria convert CYA into ammonia, then for every 10 ppm CYA that gets converted it creates 3 ppm ammonia that requires at least 23 ppm FC cumulatively added to get rid of (technical details in this post). So it doesn't take very high CYA levels to have a huge chlorine demand. My own personal experience described in this thread took around 56 ppm FC cumulatively added due to a drop in CYA of only around 20-25 ppm. So let's hope that's not the situation in this pool. When algae is present, as in this pool, the algae take up a lot of the ammonia (they use it as a source of nitrogen) which fortunately makes it easier to remove as one can catch the algae in the filter and then backwash/clean the filter.

[jrsdws]

In-process of partial draining now. I'm going to shoot for leaving about 1/3 of it's water in...skim top and use leaf basket to clean bottom as much as possible....and start filling again.

As I fill, should I start shocking with bleach and run the pump I'm draining with....only dumping back into the pool? Will this get me a good jumpstart on the algae cleanup or will it not circulate it fast enough to do anygood?

[aylad]

Any circulation will help--if you can disperse the bleach enough that you don't fade your liner (if you have one).

Janet

[jrsdws]

Yes there is a liner....pool is above ground 27' round...48" deep.

The Pool Calculator says to drain 68% of my water to lower my CYA from 95 to 30.

Right now I'm at about 50% full and still draining.....should have her down where I want later today.

Tonight I plan on adding 6 jugs of bleach while filling from two different wells AND keeping the small pump recirculating all night. Hopefully this will give me a quick upper hand on the algae and biomass that is left after raking the heck out of the bottom.

I should have it full maybe by Saturday sometime and running on main pump and filter.

I have been taking pictures along the way and will try posting them later.

[jrsdws]

Ok...settled on stopping the draining process at about 60% removal...according to the pool calculator this should put my CYA level around 45 after refilling....which is underway. I worked for a while longer raking the bottom with the leaf basket and really pulled a bunch of decomposed leaves and crud out. The water was low enough and clear enough that when the crud settled again you could see where I dragged the basket.

I added 6 jugs of bleach but decided my circulation at this point probably isn't enough to really do it any good. I think I'll just get it all filled and get the pool pump and filter running and start fresh.

The "Best Guess" chart says for +shock+ at my expected CYA level to go for 30ppm. The Calculator says that's 11 jugs!!!!

Does this sound right or should I just go for the "shock" of 15ppm and maintain that until clear?

[aylad]

I am estimating your pool volume at just over 17K gallons. A 15 ppm shock level should be sufficient (I think the other shock column is for mustard algae victims) and it looks like 4 1/2 gallons should get you just over that, if you're starting from zero. I would maintain that 15 ppm as consistently as you can, brushing daily, watching pressure on filter and cleaning as it indicates.

By the way, have you had the well water tested for metals? Iron is common in well water, and will change the course of this advice, if present....\

Janet

[jrsdws]

Iron is present in our wells, however, both wells are suitable for drinking....as determined by the county health department. For the sake of the plumbing and fixtures, though, we do run an iron filter upon entry to the house.

I am filling from two different wells at the same time. The one that supplies the house is drilled at about 130' with a fabulous supply of water. The other is the old shallow dug well and is only used for filling the pool, watering, and car washes, etc.

Please do tell my new direction as I've probably been missing something for the last 5 years!!