Green tint on the bottom

[ajb8898]

Hi, I've been having much success with the BBB method this summer but in the last two weeks I backed off how high I was keeping my levels. The pool developed this greenish coat on part of the bottom of the pool. I stir it up and it quickly floats away. I don't see any pieces of algae. It almost just seems like dirt but my sock is turning green. I've been maintaining my chlorine level back up to the regular level (10) and brushing/vacuuming several times a week but it's still not going away. The interesting thing is my kit is not registering anything growing.

CYA: 40-45
TC: 7
pH: 7.2
TA: 130

What is it? Do I need to maintain shock level to get rid of it?

[ajb8898]

Also wanted to clarify that when I checked the CYA back in June it was 50-60 so I've been keeping my TC at 10. I just did a new CYA for today and realized it's lower so perhaps I've been keeping it too high? Anyway, just wanted to explain those numbers when you see them. It makes this outbreak a little more curious as well. Seems like I've been keeping it in step with that CYA The whole time.

[CarlD]

Two thoughts: You need to test more properly for FC and CC levels, and for metal content in your water.

1) Have you shocked your pool up to 15ppm? TC can be misleading because TC=FC + CC. If you have a substantial CC reading then you need to raise your FC level to 15, not your TC. You should get an FAS-DPD chlorine test kit to measure that. If you click on my sig, you can get a link to the Taylor K-2006 or K-2006C kits, the ones we recommend. I don't get anything for it but a small amount goes to Ben to help maintain the PoolForum site. Normally, 3 1/3 gallons of 6% bleach will add 15ppm of FC to 15,000 gallons, but that much might bleach your liner.

2) My other thought is that you have a metals problem and should check for copper and iron content. If you do, then adding more chlorine will make the green worse, but the pool will be safe to use. Still, you'll have to go through metal-sequestering procedures using HEDP, but I'm not the metals person.

Carl

PS: I see that I don't have the sig link right now. Check with PoolDoc's and Watermom's posts and you should find it there. C

[ajb8898]

I do have a Taylor kit and FC is 7 and CC is 0, which is what I was indicating above that it wasn't showing any growth.

I have not shocked the pool as I wasn't sure it was required. If I get it to 15, how long do I keep it at that level since CC is showing 0?

How do I check for metals?

[CarlD]

It wasn't at all clear to me that you were using the FAS-DPD test, since you only listed TC.

You either need to get the copper and iron test kit or bring a sample to a pool store and check for metals. If there aren't metals then I'd bet you are fighting algae.

But if you now start fighting algae, you'll need to raise your FC to shock level and it can't drop much, especially overnight.

[ajb8898]

How long do I keep it at shock level since the CC is already 0?

[CarlD]

OK: First test for metals. If you have a metal problem you have to deal with that FIRST.

If there are no metals you want to raise your FC to shock level at the end of the day. Test in the morning and if it has dropped more than 1-2ppm, you need to add enough to raise it back to shock level.
The idea is that when the algae is dead, your FC won't drop. Ultimately, you want it to be able to go 24 hours without a significant drop.