We’re in our 3rd season with our fiberglass pool. Started following TFP method religiously mid-season last year.
Recently our water level dropped a few inches due to evaporation, and I realized there was now a white coating on the exposed fiberglass surface when it’s dry. It’s not above the normal water line, and it disappears when wet. It doesn’t feel rough. I started to panic and have now read though many past threads on here about similar issues. After reading others’ experiences, I’m unfortunately leaning towards oxidation. Nothing chalky rubs off or clouds the water. Can’t imagine it’s calcium.
Based on the experiences I’ve read in others’ similar posts, I’m thinking I need to raise my calcium hardness to around 300 (currently is only 150). I’ve never worried about testing CH or adding calcium to the pool before. I had double-checked with the manufacturer to ensure that my fiberglass did not contain calcium filler or whatever (I knew the right term at the time), and I felt confident I could disregard calcium hardness. That said, we have hard water and turn off our softener whenever we add water to the pool, so I was a little surprised to see that my CH is only 150.
This brings me to my first question: what would be the best way to add calcium carbonate? Would you dissolve it one measly pound at a time (I need to add upwards of 40 pounds), or should I just dump it in a bit at a time and brush it around to try to dissolve it? Could this damage my fiberglass? I bought rock-salt, so it isn’t flakes. I read about the heating issue and understand I can’t dissolve more than 1 pound at a time.
Next question: It also seems like I need to start keeping my alkalinity higher, like in the 80-90 range. I’m curious why pool math lists my recommended TA range as low as 50 for a fiberglass pool. I’d been typically keeping it around 60-70.
Last question: if I do have oxidation already happening, is the only way to reverse it by sanding? I think I know the answer to this.
Any input about any of the above information is greatly appreciated. I’m so grateful for everything I’ve learned here, but clearly my learning process is still far from complete.
Just for the sake of being thorough, my current levels are:
FC: 7
pH: 7.9 (the struggle is real folks. I add muriatic acid practically every other day)
TA: 90
CYA: 40
CH: 150
Recently our water level dropped a few inches due to evaporation, and I realized there was now a white coating on the exposed fiberglass surface when it’s dry. It’s not above the normal water line, and it disappears when wet. It doesn’t feel rough. I started to panic and have now read though many past threads on here about similar issues. After reading others’ experiences, I’m unfortunately leaning towards oxidation. Nothing chalky rubs off or clouds the water. Can’t imagine it’s calcium.
Based on the experiences I’ve read in others’ similar posts, I’m thinking I need to raise my calcium hardness to around 300 (currently is only 150). I’ve never worried about testing CH or adding calcium to the pool before. I had double-checked with the manufacturer to ensure that my fiberglass did not contain calcium filler or whatever (I knew the right term at the time), and I felt confident I could disregard calcium hardness. That said, we have hard water and turn off our softener whenever we add water to the pool, so I was a little surprised to see that my CH is only 150.
This brings me to my first question: what would be the best way to add calcium carbonate? Would you dissolve it one measly pound at a time (I need to add upwards of 40 pounds), or should I just dump it in a bit at a time and brush it around to try to dissolve it? Could this damage my fiberglass? I bought rock-salt, so it isn’t flakes. I read about the heating issue and understand I can’t dissolve more than 1 pound at a time.
Next question: It also seems like I need to start keeping my alkalinity higher, like in the 80-90 range. I’m curious why pool math lists my recommended TA range as low as 50 for a fiberglass pool. I’d been typically keeping it around 60-70.
Last question: if I do have oxidation already happening, is the only way to reverse it by sanding? I think I know the answer to this.
Any input about any of the above information is greatly appreciated. I’m so grateful for everything I’ve learned here, but clearly my learning process is still far from complete.
Just for the sake of being thorough, my current levels are:
FC: 7
pH: 7.9 (the struggle is real folks. I add muriatic acid practically every other day)
TA: 90
CYA: 40
CH: 150
Unfortunately I had not had a chance to check it in between. I don’t think my acid is bad. 
I almost did. 
