Low TA

[ricksass]

New IG pool owner in 2008. It's a SWG pool, spa spillover into pool in SW FL. I'm using the Taylor 2006 testing kit. In summer I was at 5.0 for TA now during the fall/winter months the TA has dropped to 2.0. Any reasons why the drop in TA? Is this a concern or is a TA of 2.0 in the fall/winter okay?

[chem geek]

The Total Alkalinity (TA) is measured in numbers like 60 ppm or 100 ppm, not 5.0 or 2.0 so I'm not sure what you are measuring or how you are measuring it. Are you saying that it used to take 5 drops of R-0009 reagent to turn the sample from green to red and now it takes only 2? If so, then the TA is way too low and was even too low at 50 ppm, if that's what it was.

For the TA to drop over time, you would have had to add acid. That means that your pH was probably rising as is typical with most SWG pools. You need to add baking soda over time to compensate for the drop in TA (but read the links below since you can reduce this rate of pH rise and acid addition through other means).

A lower TA will help reduce the rate of pH rise, but you need to compensate with a higher target pH and Calcium Hardness (CH) level. You can use The Pool Calculator to calculate the saturation index which should be near zero (don't forget to include the salt level which is probably around 3000 ppm for an SWG). Your saturation index may be very negative and that can dissolve plaster much faster, causing pitting and deterioration.

As for methods you can use to reduce the rate of pH rise and the amount of acid you need to add, see Water Balance for SWGs at the Pool School at Trouble Free Pool.

Richard

[Guest]

Big, big, big sorry Richard - I meant to say FC instead of TA.

I've been dealing with a bad cold the last week and all I can say is, "it must be the drugs, man".

[chem geek]

Sorry about your cold. I hope you get better soon.

As for FC dropping in the winter with an SWG, this could be due to the SWG shutting off because the water is getting too cold. Cold water does not conduct electricity as well and most SWG systems turn off when the conductivity drops below some threshold. The same thing happens if the salt level gets too low.

You may need to manually add chlorine over the winter if the SWG is off. The cooler water won't use up chlorine as quickly and if you have the pool covered then the chlorine won't break down during sunny days (even cloudy days let some UV through and that breaks down chlorine). So you may not need to add very much very often -- probably checking on it once a week will be fine, maybe even longer -- just test and see how things go.

As for whether 2.0 ppm FC is sufficient, that depends on your pool's Cyanuric Acid (CYA) level. Usually, you want the FC to be at least 5% of the CYA level to prevent algae growth. So with 60-80 ppm CYA, that would be 3-4 ppm FC. With the cooler water, a lower FC might be OK, but there's no reason to take that chance.

Richard

[Pooltech32]

I keep my pools quite low in chlorine during the winter months, around 2ppm should be fine. I actually replace the salt cells for the winter with a "blank" cell, that way your cell lasts longer.