Safe to swim in this pool? High CYA

What is floc, clarifier, stabilizer, cyanuric acid,
algaecide, brightener, dichlor, sodium hypo,
sodium bisulfate, ....??
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Posts: 1
Joined: Mon 26 Aug, 2013 21:02
My Pool: 24' AG, sand filter
Location: Richmond, VA

Safe to swim in this pool? High CYA

Postby jesseosby » Mon 26 Aug, 2013 21:45

Hi, I just moved into a house 9 days ago and the previous owners left me a messy pool from a big storm. Leaves, sticks, green algae. Pool is 24' AG, water depth is 3.5 feet, sand filter, 2.5HP two-speed pump (left running on low 24/7).

I vacuumed then added some of the previous owner's tri-chlor shock and algaecide and got the pool looking clear at least. I've been trying to get the levels straight since then, but was using those damn test strips for the first week. Now I've been reading this forum a lot, and I've ordered a TF-100 test kit which should arrive tomorrow. In the meantime, I took a sample to a pool store a few days ago. Results:

FC - 8.49
CC - 0
pH - 7.4
TA - 110
CH - 51
CYA - 167

They told me the CYA level was way too high. Previous owner used tri-chlor tablets in the pump's chlorine feeder, and tri-chlor shock. They told me to turn the feeder mix control to off and dilute the water, and sold me a few bags of 78% cal-hypo shock in case it was needed.

I pumped water out down to the skimmer level then refilled a couple of times, then took a sample back to them tonight. New results:

FC - 4.23
CC - 0.06
pH - 7.5
TA - 89
CH - 58
CYA - 149

At this rate, diluting the water enough to get the CYA down between 20 and 50 is going to take forever, and I'd like to get to use the pool a little this year before it gets too cold. So far I've held off on using it for fear of it not being safe.

I read something mentioned about bringing FC up to 7% of CYA. Is that an acceptable short-term alternative to bringing the CYA down? 7% of my 149 CYA would be 10.4, and from using the pool calculator, it looks like a 12oz bag of the 78% cal-hypo I have would get me there. Would that, along with bringing up the TA and CH, give me safe water to use for the next few weeks or so? Then I can worry about lowering the CYA when I close the pool?

Thanks in advance

chem geek
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Joined: Thu 21 Jun, 2007 21:27
Location: San Rafael, California

Safe to swim in this pool? High CYA

Postby chem geek » Wed 28 Aug, 2013 21:08

Yes, your plan is reasonable. You probably won't even notice the FC level being that high since the active chlorine level is proportional to the FC/CYA ratio so is roughly equivalent to a pool with only 0.07 ppm FC and no CYA. Do not bring up the TA. There is no need to do that and it will just cause your pH to rise when using hypochlorite sources of chlorine. You only need a higher TA when using acidic sources of chlorine such as Trichlor or Dichlor (which is net acidic when accounting for chlorine usage/consumption). You should also leave your CH alone since your pool is an above-ground pool that I assume has a vinyl liner so you have no plaster or grout surfaces to protect with calcium carbonate. Your use of Cal-Hypo will increase the CH level anyway. For every 10 ppm FC added by Cal-Hypo, it also increases CH by at least 7 ppm.

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