I recently drained and refilled my 16000 gal outdoor (inground, gunite/plaster) pool, due to high CYA (300 ppm), high TDS (3700) and high phosphates (600). Immediately after refilling, my TDS is now 450, and phosphates is 0. My CH level is now 210. After refilling, I added enough CYA to get a starting level of 30 ppm.
After refilling the pool, I stopped using the tri-chlor tabs in my feeder, to avoid CYA buildup, and started using liquid chlorine (10%) for regular dosing, and find that I have to add the equivalent of 2 ppm (for my pool) almost every day.
I see that the super-chlorination shock value for my CYA level is 12 ppm of chlorine. For my pool that requires 1.8 gal of liquid chlorine, or $9.40 per shock treatment (at Leslies prices). As an alternative, i started using Leslies Fresh N clear (potassium peroxymonosulfate 38%). Their recommended regular dosage for my pool is 1.6 lbs, which costs me $6.70, based on their price for a 25 lb bucket. So it seems that the non-chlorine shock costs less, and swimming can resume much more quickly.
1. My first question is whether using this non-chlorine shock on a regular basis is as effective as doing the super-chlorination shock? We don't swim everyday, so we can tolerate waiting a few days for high chlorine levels to subside. We usually have swimmers no more than 2-3 days a week in summer.
2. My second question is what is the best way for me to do regular chlorination? I wanted to avoid the tri-chlor tabs, and just use them for short periods when we are away on vacation and there is no one to do daily testing and chemical maintenance. For the same reasons, I don't want to use di-chlor powder on a regular basis. That leaves me with the choice of liquid chlorine or calcium hypochlorite. The guy at the pool store said regular use of liquid chlorine will cause an excessive buildup of TDS. He said it would be better for me to use calcium hypochlorite. (The only solid I can think of from the liquid chlorine would be sodium - does that count as part of TDS?) When I told him I thought regular use of Calcium hypo would cause excessive buildup of calcium, he said that would not be a problem and could be mitigated by adding something to keep the calcium from forming scale. He said the TDS from bleach would be a problem. I don't necessarily believe anything they tell me at a pool store, So what is better: using something that increases calcium or something that possibly increases my sodium or TDS?
Because my free chlorine levels fluctuate so fast, requiring me to tend to the pool every day, I find that I can add enough to get a FC ppm of 2 late in the afternoon, and then less than 24 hours later it is almost 0. So even if I tend to it every day (sometimes several times in a day) I can hardly keep up with the chlorine dissipation. I'm almost tempted to go back to the automatic tab feeder method, and just accept the fact that I will have to drain the pool in less than a year due to high CYA. The cost to refill the pool can be less than the cost of a lot of chemicals, but I hate to contribute to the water shortage problems in our drought area.
On one of the TFP forums I read that, for each 1 ppm of chorine that is added from tabs, there will be 0.6 ppm of CYA added, so it won't take long before I have to drain it again if I do this. I have read the info on TFP about the required FC levels being proportional to the CYA, so I realize I'd need to monitor my CYA and increase my chlorine dosage accordingly.