Disappearing chlorine...

[nthach]

The pool I was working on getting algae free is doing great, I had to tweak a few levels but the Cl is disappearing! The last 2 times I checked the pool with a OTO kit, it barely registered. I use a Taylor FAS-DPD to verify the HTH kit, and there is between .5-1 ppm of free Cl and zero combined. The owner is adding 1/3-1/2 gallon of 6% bleach daily - but I don't think it's enough for a 17K gallon pool. I just added in 1lb of 73% cal hypo and a cup of 54% cal hypo resulting in a free Cl of 7.5 per FAS-DPD test. The CYA level was at 60 last week but we added water in the pool, and now CYA tests at 40.

The pool's in the sun for most of the day, and so I'm wondering what to do either a) more bleach or b) supplement the bleach with a HTH skimmer tab to keep the free Cl a bit more stable.

[Watermom]

In a 17,000 gallon pool, each quart of 6% bleach is only going to raise the cl by slightly under 1ppm. So a half gallon is only going to add a little under 2ppm. If he is only adding 1/2 gallon daily, that is not enough. With a cya of 40, the cl needs to stay between 3-6 ALL the time and the shock level is 15. So either he is going to need to use a larger daily dose of bleach or supplement with cal-hypo. I wouldn't suggest using triclor as his CYA is already 40. Don't really want it higher and the trichlor will increase it.

We really could use a complete set of current water testing numbers to better advise. Also what type of pool is this. It would be better to know these things first before recommending the use of cal-hypo. And, please remind us again -- are you in the pool industry or just helping a friend with his pool? (We have so many members and so many different threads that it is hard to remember.)

Thanks.

EDIT -- Since he has let his cl drop so low, I would suggest shocking it up to 15 just in case a bloom might be trying to get started since you can't always see it at first. Probably doesn't but it is cheap insurance just in case. Easier to do this than to clean up algae later.

[nthach]

In a 17,000 gallon pool, each quart of 6% bleach is only going to raise the cl by slightly under 1ppm. So a half gallon is only going to add a little under 2ppm. If he is only adding 1/2 gallon daily, that is not enough. With a cya of 40, the cl needs to stay between 3-6 ALL the time and the shock level is 15. So either he is going to need to use a larger daily dose of bleach or supplement with cal-hypo. I wouldn't suggest using triclor as his CYA is already 40. Don't really want it higher and the trichlor will increase it.

We really could use a complete set of current water testing numbers to better advise. Also what type of pool is this. It would be better to know these things first before recommending the use of cal-hypo. And, please remind us again -- are you in the pool industry or just helping a friend with his pool? (We have so many members and so many different threads that it is hard to remember.)

Thanks.

EDIT -- Since he has let his cl drop so low, I would suggest shocking it up to 15 just in case a bloom might be trying to get started since you can't always see it at first. Probably doesn't but it is cheap insurance just in case. Easier to do this than to clean up algae later.

I'm helping a friend with his pool. I'll do a another test tomorrow. The pool is a concrete/plaster pool - so the pool needs Ca.

[docsobeck]

with a pool that gets all-day sun, a solar cover is very helpful in decreasing the chlorine demand. my cover doesn't do a whole lot to warm the pool in the summer - in fact it warms up more during the day with the cover off - but it probably cuts my chlorine usage in half. (for the record, the solar cover holds in the heat at night far better than it generates heat during the day. which has nothing to do with what you asked...)

anyhow, when i was using 6% bleach in my 24,000 gallon pool, with the solar cover on when the pool wasn't in use, i was putting in 48 oz. each night and that would keep me at a pretty consistent 2 - 2.5 PPM. i had to use twice that over periods when i got too lazy to haul the cover on and off.

[chem geek]

The type of cover seems to make a difference with clear covers not doing much to block the UV in sunlight while blue covers seem to block some if it (though not all). So for protecting the chlorine in the water, the blue covers do a better job. Even better for chlorine protection is an opaque cover, but then you don't get much heating from the sun during the day.

[polyvue]

The type of cover seems to make a difference with clear covers not doing much to block the UV in sunlight while blue covers seem to block some if it (though not all). So for protecting the chlorine in the water, the blue covers do a better job.

Is this an educated guess or a result of experience / experiment? I remember this was discussed last year (different forum) and I decided to replace my blue solar cover with a clear one -- it's on the pool now but not enough time has elapsed for me to be able to draw any meaningful comparisons.