Fiberglass pool and HIGH HIGH hardness and unscrubbable ring around the pool


New member
Jun 8, 2021
Tucson, AZ
So our fiberglass pool is just over a year old. We purchased fiberglass primarily for it's supposed ease of maintenance. We are new to the chemical balancing and haven't been religious about it but are monitoring it much closer now. So info you need to know:
1. We have a well with extremely hard water which rapidly evaporates from our new pool in Tucson, Arizona.
2. We have a definite ring around the water edge that is not wiping off. We have tried green scour pads, magic eraser, microfiber rags and it isn't budging. Our pool is white colored but there is a tinge of beige to the ring so it is visible.
3. The sides of the pool in many places are not smooth like they used to be. We run our pentair rebel all the time so the floor of the pool seems to be okay, but much of the walls it doesn't attach to consistently. I think that is why some parts of the wall feel smooth whereas other places it does not. Perhaps the vacuum gets the calcium buildup when it is new?

But back to our hardness problem... I can't see our calcium levels going down no matter how we post-treat the water. We keep pumping in hard water to replace the evaporated water. I am just a novice, but it seems to me that I need a way to remove the calcium. From the reading I have done it seems that RO cleaning services do that- filter the water and they put it back in, then they balance the water chemicals. However, I just had one company say they don't service fiberglass pools... but don't know why yet.

My big questions are:
1. If we ever get the pool balanced, can we run the water line to the pool through a RO system BEFORE it gets to the pool in the hopes to filter out most of the hard water (calcium)?
2. Would Pool Flock work for this, even temporarily?
3. We were told by the pool manufacturer that muriatic acid would take the ring off easy... but how? I have scoured youtube/internet and can't find practical scrubbing apparatus and methods in which to apply muriatic to a ring in a pool full of water.

Any help and advice would be greatly appreciated.

Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
Jun 22, 2014
Texas, San Antonio/Marion, South-Central Area
Pool Size
Salt Water Generator
SWG Type
CircuPool RJ-45 Plus
Welcome to TFP! :wave: So we understand the hard water history in the area, but we also need to ensure all areas are considered. To do so I would submit the following to you:
- We need a full set of water test results. At TFP we recognize either the TF-100 (link in my signature) or Taylor K-2006C as the most reliable user-friendly kits for home use. But we need to see your numbers.
- Post a couple pics so we can see the discoloration
- Update your signature with all of your pool and equipment info. See mine as an example.
- If it truly is calcium, the manufacturer will have you do a test, much like they did with me. You can lower the water level to expose the first step and pour muriatic acid on it. If it's calcium, it will react (fizzle) right away. If it doesn't there's a different issue.

I'm not an expert on RO, perhaps @JoyfulNoise would like to discuss that with you. But I can also assure you that with proper chemistry, we can show you how to at the vert least mitigate the potential of calcium scale in your pool. But we really need those test results first.



Mod Squad
Gold Supporter
LifeTime Supporter
Jan 17, 2012
Evans, Georgia
How high *is* your calcium hardness??
What are these test results-
Salt if applicable

I do not believe the water line line is the hardness but rather a problem with the gel coat. Hardness would be uniformly a problem, although it does often appear yellow/brown dirty.

Pool Floc!?!?! Pool FLOC doesn't work well for ANYONE for any reason. We never suggest anyone use it.

Maddie 🐞


TFP Expert
Platinum Supporter
May 23, 2015
Tucson, AZ
Pool Size
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
You need a whole-house water softener on that well or water treatment system. Wells in Tucson can be highly variable in their mineral and iron content - some wells produce very soft water, others produce water that looks like concrete slurry pouring out of the faucet. If the well is really bad, you may need a very sophisticated whole house RO system with a 500 gallon storage tank and variable speed repressurizing pump into your main plumbing line.

I suggest you contact WaterTec of Tucson and get some advice on what to do. Leigh, the owner, is highly knowledgeable and can quote you a system to handle your needs. It’s going to be pricey though so be prepared for sticker shock. However, when you factor in how much damage untreated hard water can do to your home’s faucets, the water heater(s) and your now scaled-out pool, the system will benefit you greatly.

The others above have you covered, follow their advice.
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Bronze Supporter
May 29, 2019
Welcome to TFP! I am a fellow fiberglass owner.

I agree with Texas Splash, I would highly recommend getting a good test kit and understanding your water chemistry before trying any remediation efforts. The first year I owned my pool (2018) I was following pool store advice. I was adding copper based algaecides to fight algae problems because my CYA was so high that the chlorine couldn't keep up. I also followed pool store advice and used powered shock once a week.

I ended up shocking the copper out of suspension and it stained the walls of my white fiberglass pool. I wanted to throw up I was so distraught.

Here is the good news. The next year I found Trouble Free Pools after opening my pool. Following the advice here I got my pool water chemistry balanced and where it should be, and the copper staining just literally went away. I've had no issues with my pool since I found this place. I am not saying you do not have hard water that is causing your issues, but what I am saying is that trying to remediate that without first getting your water balanced and knowing what you are dealing with will cause you a lot of stress.

The goodness is that if you get a proper testkit then you can test your well water for CH too so you know what you are dealing with starting from the fill water.
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