Fiberglass pool help


New member
Apr 18, 2019
Yuma, AZ
Hello TFP, I’ve had a home with a previously installed 12,500 gallon fiberglass pool for 4 years. The first two seasons I had issues with low PH, I tested for metals and had high iron. We then removed the pool heater and replaced about half the water. The iron went down but was still there so last year we drained about 2 feet of water 4 times (didn’t want the shell to pop out) and all levels were perfect. Now it’s time to open again and I have low ph, low alkalinity, and high CYA but no metals. What I’m reading here is that it’s from the tri-Chlor pucks. I’ve read that fiberglass has no acid demand like plaster does so my question is this: how do I use liquid chlorine? How much do I use and how often? Will the liquid chlorine be damaging for fiberglass? I live in AZ where it gets to 120, liquid chlorine honestly scares me but I see from all of you that the pucks just cause headaches. I’m planning on draining some water to get the levels normal and then switching. Thank you!


Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
Laughlin, NV
Welcome to the forum.
Regardless you will be using acid. Your water is from the Colorado River, like mine. TA of 130 ppm.

How do you test your water chemistry. You need your own test kit. I recommend the TF100.

Once you get your kit post up the results and we can guide you on a path forward.

Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
In addition to Marty's notes, remember that regardless of shop-talk at the pool store or by a salesman, chlorine is chlorine. Doesn't matter if it's in bags, pucks, or liquid form. Free Chlorine (FC) is chlorine. What DOES matter are the by-products and/or potential side effects form each of those. Aside from a salt water generator, we like liquid chlorine (aka regular bleach) best for daily use because it has next to no by-products and no side effects. It's pH neutral. By that we mean any amount of bleach added in significant amounts enough to potentially raise pH, will be lowered and the pH will return to its original spot. Once you know your current FC, you will use the PoolMath tool or app to add the appropriate amount of chlorine by pouring slowly near a return jet(s).

Stick around, we'll show you more as you learn more about TFP. Welcome! :wave:
ABCs of Pool Water Chemistry