Chronic Low TA

[Alexania]

Hey, hoping someone can offer some advise.

We installed a (15,000l) fibre glass pool about a year and a half ago. At the time of installation my TA was around 110. From there it rapidly dropped. At that time the Ph was usually too high by a small fraction so i was adding a small quantity of acid on a weekly basis to fix the Ph.

TA kept dropping though, Id get it back to expected levels then within a week itll be back down to 60 or so. At one point I didnt keep up with my regular Alkalinity Inc additions and it just bottomed out to pretty much zero.

I fixed it -again- (and fixed the hardness and metal removed etc) and but it just drops again and the last couple months has been coupled with a low Ph as well. Its currently sitting at 40, Ph of like 7.0.

I wanted to add soda ash but saw that's not recommended for fibreglass.

At this point my pool maintenance consists of a chlorine floater and weekly (or more) Alkalinity Up additions. Which seems weird.

Any idea what could be causing this?

[Alexania]

Just to add, looking at the chlorine floater I'm using, it appears this is its composition, any chance it could be the cause (I'm going to switch to weekly additions of granular chlorine in any case and see if maybe it changes anything)?

Trichloroisocyanuricacid: 75% - 80%
Sodium Dichloroisocyanuricacid: 10% - 15%
Aluminium Sulphate: 5% - 12%
Boric Acid: 1% - 4%

[Poolaroo]

Some fill water is prone to low alkalinity. The tablets in your floater also reduce the pH and alkalinity.
Granular chlorine is usually eithe dichlor, which is mostly pH neutral but has a lot of stabilizer, or cal hypo which is alkaline but adds a lot of calcium to the pool which can result in scale later on.

You would be best off using bicarb (from the supemarket is fine) to raise the alkalinity, and unscented bleach for the chlorine.
Why can you not use soda ash?

Because you have been using the stabilized tablets there is most likely a buildup of stabilizer, so taking a break from stabilized chlorine is a good idea too.

Joe

[Alexania]

Some fill water is prone to low alkalinity. The tablets in your floater also reduce the pH and alkalinity.
Granular chlorine is usually eithe dichlor, which is mostly pH neutral but has a lot of stabilizer, or cal hypo which is alkaline but adds a lot of calcium to the pool which can result in scale later on.

You would be best off using bicarb (from the supemarket is fine) to raise the alkalinity, and unscented bleach for the chlorine.
Why can you not use soda ash?

Because you have been using the stabilized tablets there is most likely a buildup of stabilizer, so taking a break from stabilized chlorine is a good idea too.

Joe

Thanks for the response! I've checked my cyanuric acid and I'm luckily still on the low side of ideal (my pool gets a LOT of sun). Only granular I can find is cal hypo and I honestly doubt if I'm up for dosing my pool on a daily basis. I'll continue with the bicarb and keep an eye on the stabiliser levels.

I'm unsure about the soda ash, was going to buy a pack of it the other day and saw on the back it said that soda ash is not recommended for fibreglass pools and that they recommend using bicarb to raise the Ph instead.

[chem geek]

Trichlor is ACIDIC and will lower the TA over time. For every 10 ppm FC added by Trichlor, it also increases CYA by 6 ppm and lowers TA by 7 ppm.

You should keep your TA at a level where your pH isn't rising (if the pH is rising, your TA is too high) and you can maintain the TA level with baking soda or if you need to raise the pH as well you can use soda ash. I don't know where you heard that soda ash should not be used with fiberglass -- that isn't true. Always add concentrated chemicals slowly over a return flow with the pump running and then lightly brush the side and bottom where you've added the chemical.