Indoor pool chemistry

Waterhouse

New member
Jun 9, 2019
3
Cotswolds UK
We bought a house two years ago that happens to have an indoor pool, not the reason we bought it. The pool is 20 years old and hadn’t been used for perhaps ten years. We changed the pump, cleaned the filter, added a UV lamp and got it working. Then it got complicated because everybody has opinions on outdoor pools and nobody knows about indoor pools, especially the professionals. So it’s been a voyage of discovery.

The pool is around 45000 litres is heated and has an excellent cover. It almost never gets any sunlight. My current chemistry looks like this
free chlorine 3.1
CC 4.2
pH 7.4
TA 240
calcium hardness 350
CYA 27

I never get algae and the water is clear. We live in an area of limestone so the water is naturally hard. The pH rarely moves and once I realised that stabiliser was pointless the CYA is stable too.
My question is around the CC. It is invariably above the FC and marches in lockstep with it. But we have no smell of chlorine or stinging eyes. Is this ok?
 

Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
Welcome to TFP! :wave: In some cases, an elevated CC level is related to the type of chlorine product used. Can you tell us how you chlorinate the water? You have a UV but I'm guessing no ozone product? Can you update your signature please with all of your pool and equipment info? It will help in future posts. As for stabilizer (CYA), it's good you have some in there now. Here at TFP it's common to have about 20 ppm of stabilizer for an indoor pool, not so much for sun UV protection, but to buffer the chlorine so it's not too harsh.

We also use a product here called the PoolMath APP which allows users to enter (and save) their water testing and to see what items may need adjusting. With hard water and a heater, you need to watch both for scale and erosion to the heater. That tool should help. Below in my signature are some Vital Links. I would recommend bookmarking and reading them for easy reference as well. If you decide later you'd like to work on lowering that TA a bit, below is a link to help.

 

Flying Tivo

Well-known member
Jan 24, 2017
1,889
Monterrey, NL, Mexico
CC get broken down by the sun's UV rays. It also difficult for CC to dissipate if the pool is covered most of the time. You can try to remove the cover for longer periods of time or you can get additional UV lamps to help you break down CC.
 

Waterhouse

New member
Jun 9, 2019
3
Cotswolds UK
The uv lamp is concealed so it’s hard to tell but it was new two years ago so should work. Not sure how to check it.

The water here is hard. The water company says it has total calcium hardness of 284 ppm and total calcium alkalinity of 219 ppm.
I keep the pool covered except when it’s in use, which is usually no more than half an hour a day. Keeping it covered keeps the heat in and keeps the humidity in the pool house down.
 

skybloke

New member
Apr 25, 2019
4
N. Bucks, UK
The uv lamp is concealed so it’s hard to tell but it was new two years ago so should work. Not sure how to check it.

The water here is hard. The water company says it has total calcium hardness of 284 ppm and total calcium alkalinity of 219 ppm.
I keep the pool covered except when it’s in use, which is usually no more than half an hour a day. Keeping it covered keeps the heat in and keeps the humidity in the pool house down.
Hi Waterhouse. Just seen your posts so thought I'd contribute to your thread as I have a similar sized indoor pool/cover arrangement and I'm in the Anglia (UK) water district (source CH280 TA180). Years ago I used 200g Trichlor tabs in a feeder now its Cal-Hypo. I put your figures into PoolMath and got your CSI about 0.4 (assuming 29 degrees C) which is on the high side I reckon and you risk/may experience cloudiness in the water at some point and/or limescale deposits on the cover/equipment and surrounding area. Your high TA will be strongly resisting the pH from moving. Personally I'd get the TA down (mine's about half your value) using acid to get to pH 7.2 and then aerate. Lots of info on the forum about that method. If you turn the heater off through the winter, as I do, then also be aware of how water temp effects CSI. For example your present figures at 12 degrees C give a much more respectably balanced 0.1 CSI. Don't use test strips and, like you, I keep the FC around 2-3ppm for a 20-30 CYA level. If my CC was genuinely 4.2 I'd be slamming. How are you measuring that? DPD1&3? Are you absolutely sure its not TC that is 4.2ppm in which case CC would then be about 1ppm). I haven't had to slam for several years using the TFP method although my pool only gets light use these days. Hope that all helps.