I just bought a house month ago with a 21k IG Fiberglass pool, with motorized water proof cover that's about 10 years old. I didn't really want a pool, but it's there, and it's very nice, but the previous owner (PO) only used the trichlor tabs, and was constantly shocking the pool. I've spent a bunch of time reading here, and ordered the TF-100 test kit, which I got last week. He had the K-2005 kit, but some of the reagents were low or out, plus the FC was too hard to read for me, and trying to accurately match the colors.
I knew the CYA would be high, due to years of trichlor usage, but since TA was also very high (~240) so several times while vacuuming I wasted it and lowered the water about 8" and then refilled it with softened water. Sat I tested and here's what I had.
FC = 3.5
CC = 0.5
TC = 4.0
TA = 190
PH = 7.5
CH = 220
CYA = ~120
Obviously, my TA and CYA are high but I thought it might be considerably higher. A couple of weeks ago I took a sample to the local pool store, and they said CYA of 90, but they weren't concerned about either it or the high TA, which they said was 120. Go figure, their fancy, dancy computerized strip reader isn't very accurate, that's for sure.
A month ago my CH was about 320, but with the addition of several thousand gallons of soft water, it's come down quite a bit, though I don't know if I should go much lower based on what I've read.
I used soft water because the well water is very hard at 35 grains, or ~612 PPM hardness, with 5 PPM of Iron, which is the real kicker. The pool has some iron stains, because the PO said he opened with well water this spring as he didn't want to pay the cost of using softened water.
For now, I dumped 3.5 gallons of 12% CL into the pool, which should raise it close to the 13.6 target for FC, plus 2 quarts of sequestrant to see if that helps with the iron stains. I haven't been using the trichlor tablets for about 3 weeks, and have added CL several times, but not this much. It appears that I have some algae causing the CC, but didn't want to add enough CL to get to the shock level needed at CYA of 120. Given that the CL has been around 3 or 4 for the past month, I guess I'm not doing too bad if I didn't get more algae than that. The water is also very warm, at about 92 F due to the cover I suppose.
I know that eventually I need to replace around 2/3 of the water in the pool, but I don't know that I want or should use all softened water to fill it again. On the other hand, I don't want to use straight well water either, due to the high iron. I also want to borate the pool, but figured I need to get the CYA and TA fixed first, or I'm just wasting a lot of Borax.
So I have a couple of questions.
Will a considerably lower CH cause problems with a fiberglass pool? If I replace about 12k gallons of water with softened water, I would expect CH to drop down around 100 or so. Will this cause any issues? Or do I need to add something to bring it back up again to avoid easy staining?
I also read that one of the best ways to deal with the existing rust stains is to use Ascorbic acid after the water is below 65 degrees and allowing the FC to drop to zero, so that's something for this fall, say Oct, I assume before closing it.
What would the experts recommend for this pool? There is only about a month or so left of this swim season here in northern Indiana, so my thoughts are too keep it going now, and then deal with the other issues this fall. Given that I technically should replace about 2/3 of my water, I suppose I could actually save quite a bit of refill water if I kept them separate using a large tarp like someone else did that bought a foreclosed property where the pool was a swamp. If I drain and refill at the same time, there will be constant mixing, and a lot more refill water will be needed to replace a given quantity of the water.
Will doing this also lower my TA down to where it should be? What is the ideal TA level? The well water is very close to neutral at 7.0, but the PO used lots of PH Up to keep his PH up, hence the high TA levels.
I want to go straight BBB with borates, as that should help a lot and make things much simpler. Now I'm spending too much time taking readings and trying to figure out the correct steps to take. Of course, part of that is educational, with a lot of time reading this website. Thanks, as it sure makes way more sense than listening to the "experts" at the pool store. Good grief, they have lots of different chemicals and ****, and they aren't concerned about any of my readings. "Why, just dump in some other chemicals and that will take care of it"! They don't even seem to know that high CYA means that FC levels have to be very high too, and just recommend the normal 3 - 4 ppm of FC, and use an algae preventer. Yeah, and I can see that you will be constantly chasing your tail and more importantly, spending boat loads of money treating one thing or another.
Sorry, I know it's long and a lot of info, but I wanted to try to give the whole picture in one shot. Wish I could easily haul in 12k gallon of iron free water instead of waiting on the well pump. It takes forever to refill the pool with a garden hose, at about 1" per hour, and lot's of salt for the softener. Good thing I have a Kinetico dual tank system so you can use soft water out of one side while the other regenerates.
Thanks in advance