How important is Calcium Hardness in Fiberglass Pool?

[Geoff2005]

Hi All,
This is my first post, looks like a great forum. I have read some parts of the forum and was convinced to get a good test kit rather than going to the pool shop thus I have acquired my own personal test kit. So after doing doing the first run (result accuracy may be a little off till I get the hang of it) I measured

pH 7.4
CH not detected (in the 2 stage test the first stage indicated no CH)
FC 2.0
CYA 30
TA 40

and using a cheap digital TDS meter 1500.

Before I added anything to lift the calcium hardness I wanted to establish why as what I have read focuses on impact on cement and plaster based materials.

Geoff

 

[MarianParoo]

See this link: Pool School - Recommended Levels

 

[Jezza]

Hi Geoff,

Welcome to TFP! I'm just down the road in Bunbury.

CH is more critical in cement/plaster pools as it protects the calcium in the pool surface from pitting. Some fibreglass pools are made with a gelcoat which also has calcium carbonate and therefore to a lesser extent it needs to have CH added as well. This is the case with my fibreglass pool. Can you find out whether your pool has a gelcoat by contacting the manufacturer?

Also your FC level is on the minimum level for your current CYA level and if you let it drop much lower than you will risk an algae outbreak especially now that the weather is warming up here. So maybe get it up to around 5 for that level of CYA but you will want to get your CYA up to about 50 in due course. I would monitor your pH by testing daily as your low TA may cause it to fluctuate and you certainly do not want your pH levels to go outside the recommended levels. I'm assuming that your Chemigem isn't the model with the pH auto feeder.? Read up on Pool School and this will give you a really good grounding.

 

[Geoff2005]

Oh thanks for the quick replies.

@Jezza Hi neighbor.
The pool is ~15 years and made by Buccaneer. I assume was typical gelcoat/cloth resin construction. I'll just target the recommended level in MarianParoo's link.
Just starting to look at pool for this summer, the desired chemicals seem to dilute with the winter rains.
The Chemigem does both chlorine and acid dosing, though I have found the sensor is prone to inaccuracy with foreign matter catching or building up on the probe and I usually give it a rinse in acid this time of year.

 

[Leebo]

As mentioned above there are a few times that calcium is needed in Fiberglass pools, so to play on the safe side we suggest maintaining 220-320ppm calcium in the water to avoid any issues. Unfortunately I do slightly question the Australian test kit you have purchased as it's somewhat unlikely you have zero Calcium in your water. Can you please explain to us what you see as your preform this test? If you do start to add any calcium based on this kit I would HIGHLY suggest you tiptoe to your "goal" and only add a small amount at a time. It's FAR easier to add calcium than it is to remove.

 

[otter86753]

Before I added anything to lift the calcium hardness I wanted to establish why as what I have read focuses on impact on cement and plaster based materials.

Geoff

Calcium can also be part of keeping your CSI at the correct level. I too have a fiberglass pool and to keep my CSI where I want it, I have to increase my Calcium to 300 and raise my PH to 7.8 to balance keeping my TA at 60 so i don't have PH creep. It really is finding the "sweet spot" that your pool likes and each pool is unique.

 

[Patrick_B]

I'm obviously not familiar with that water, but it is very unusual for most water in the work to be free of calcium. Hardness can vary wildly, but none is very rare.

May I ask what you mean by the first and second stages of the CH test Geoff?

 

[Geoff2005]

Hi All,
Thanks for the further feedback on CH in relation to Fiberglass Pools.

Re CH test.
Test kit instruction said add drops in first stage and sample will turn orange indicating calcium, my sample was more like purple/black after adding stage 1 so I didn't bother adding stage 2 reagent.
I see here though the instructions may be wrong Aussie test kits and hello.
So I will try test again with different target colours.

 

[Geoff2005]

Just redid CH test, I see it is 3 step not 2 as I had recalled, I just didnt do last step as colour was not orange.
Anyway redoing and using change from red to blue (not orange to green as per instruction) I got a result of CH = 125.

 

[otter86753]

You might also look at this thread Newbie From Perth Western Australia. - Page 3 post 50 as there might be an issue with the test kit (if you have the same one).

 

[Patrick_B]

Orange to Green would be a TA test. A CH test should always be Pink/Red to Blue/Purple. I'll check the links, and may post back afterward.

update:

It seems like they are really careless putting this together after seeing the other thread. TA test instructions for Calcium. That's an unacceptable oversight in my opinion. Wow.