Hi – I’m new to this website, and new to pool maintenance. Before I get to ‘the problem’, here are some basic facts and history:

19,100 gallon pool (cement + pebbles), 6 years old; System 3 Modular Media Filter, Polaris pool-sweep.

Acquired by us 4.5 years ago. Since then it has been looked after by the same private-contractor pool guy (let’s call him Tom). Tom told us that the Nature 2 Professional G Inground Purifier that the previous owners had installed is unnecessary, and that it is better to just use chlorine. He comes once a week in the summer and once a fortnight during winter to test the water and adjust the chemicals. He also put in one of those little floating baskets with chlorine tablets. He cleans the filter once a year (when asked about this, he said that the filter works better if it is cleaned only once a year).

So basically we left him to it, but it seems that we now have a problem. Tom says the pool suffers from chlorine lock and will probably have to be partially drained and refilled. I have spent considerable time reading on your wonderful website, but even though I now know a little more about pool chemistry, I am getting more confused by the minute.

Tom added chlorine on Tuesday, but I do not know what the test results were then (other than he told me that the chlorine is neutralised very quickly and he keeps having to shock the pool really hard). I had the water tested at a local pool store on Thursday and was told that total dissolved solids = 2.1 (apparently this is high - should be 0.19 max?); pH = 7;
Chlorine = 3; CYA = 90-100.

I bought a kit and re-tested some of this today: Free chlorine = 1.5 (unchanged when testing for TC); pH = 7.3; T/A = 60. By the way, the water looks clean.

The water was very warm but since the solar heating was turned off four days ago it has cooled down considerably (sorry, don’t know the temperature – just noticed the thermometer is broken…). We are in California – 90+ days are the norm at this time of the year.

I would be very grateful for any suggestions. TIA!