Effect of Rainfall on TA

[smcrea]

This is the first winter that I've had my pool. I live in San Diego so do not winterize my pool.

I'm new to pool maintenance, but am discovering that each season offers it's own maintenance challenges.

We just has a huge amount of rain. I was shocked by the amount that my TA dropped by. Before the rain my TA was just over 90. After the rain I was down at 60.

I noticed also that my Ph had edged upwards to around 7.8. My Chlorine generator is off at the moment, so I'm wondering what conditions with the rain are causing my TA to plummet downwards and my Ph to edge upwards??

I'm not looking for a remedial action.. I dealt with the TA with baking soda and then a couple of days later tweaked my Ph back down with acid. What I'm looking for is 'why' does the rainfall have this effect?

Thanks,

Steve

[chem geek]

Did the rain overflow your pool water? If so, then it diluted everything in the water thereby lowering the Total Alkalinity (TA) and the Calcium Hardness (CH). Rain has very little TA (around 10 ppm, depending on pH) and virtually no CH.

It's a bit surprising that it diluted by that much -- if your pump isn't running or you have poor circulation then the surface water may be more diluted then the water at depth.

As for the pH, it can go either way depending on rainfall pH though it takes quite an acid rain to lower the pool's pH. Normally, the rain will simply increase aeration of the water and that normally has the pH rise since the water is over-carbonated and outgassing of carbon dioxide causes the pH to rise.

[smcrea]

Thanks for your reply,

The rain most certainly did cause my pool water to overflow through the appropriate overflow pipe. I think that this was a lot because my 3000ppm salt level dropped to 1800ppm!!!! showing that my water was really diluted.

So if rainwater has a TA of around 10 then this would answer the question. Also the carbonation that you mentioned because of the rain answers the question on Ph.

Thanks!

Steve.