Do I need to increase CYA?

[Ke]

I have a salt water fiberglass pool with a SWG and an automatic cover. We only use the pool for about 4 times a week, about 3 hours each time, otherwise the cover is closed. Here are the numbers:

salt: 3200
FC: 2
TA: 100
TH: 250
PH: 7.5
CYA: 20
SWG setting: 20%

So far the only problem was metal stains which were cleaned up by ascorbic acid treatment. The water is always sparkling. I was wondering if there is a need to increase CYA since most of the time the pool is not exposed to sunlight. I don't want to increase FC too much as it may promote metal stains.

 

[Guest]

If the pool is NOT an indoor pool it would be a good idea. You will have better pH stability because you will be able to turn your generator output down. See this thread:
viewtopic.php?f=21&t=3663
Also, calcium hardness levels ARE important for fiberglass. There is evidence that proper calcium levels can help prevent staining and cobalt spotting. I noticed that you did not list calcium hardness.

 

[frustratedpoolmom]

Actually OP lists TH at 250...

WIth an SWG, the recommended level for CYA is 70-80, but you should also check your manufacturers recommendation so that you don't void any warranty. See the article about recommended levels for SWG pools in Pool School... you can run your pool with a CYA of 70 and a FC of 3, at the minimum. As long as you keep your PH and TH in range, a FC of 3-5 is unlikely to stain your pool, but if your metals are high, consider a maintenance dose of metal sequesterant to help prevent staining.

 

[Guest]

Actually OP lists TH at 250...

Total hardness is a useless test for pools and indicates that the testing was done with strips. Strips cannot test calcium hardness, only total (calcium and magnesium) hardness. Calcium hardness numbers are still needed. Total hardness is going to read higher than calcium hardness and from the number posted I can pretty much be sure the CH is a bit too low. I stand by what I said before.

 

[frustratedpoolmom]

Actually OP lists TH at 250...

Total hardness is a useless test for pools and indicates that the testing was done with strips. Strips cannot test calcium hardness, only total (calcium and magnesium) hardness. Calcium hardness numbers are still needed. Total hardness is going to read higher than calcium hardness and from the number posted I can pretty much be sure the CH is a bit too low. I stand by what I said before.

That's what I get for skimming. My bad, I stand corrected.