I’m getting ready to prep my pool for closing. I’m trying to decide if I’m going to add polyquat before closing like I usually do or close at SLAM level this year since the water temperature is down to 60 degrees already. The company who installed the pool 20 years ago says that closing at SLAM level with a FC of 16 ppm would be harmful to the gelcoat since FC levels will remain high all winter. The gelcoat in my fiberglass pool has been chalking terribly this year and the calcium level is only 200 so my pool pro thinks that the chalking is due to deteriorating gelcoat and not scaling and it will need refinishing in a few years. I would like to postpone the refinishing as long as possible since it is very expensive so should I follow his advice and use polyquat? I haven’t had much success with polyquat in the past and usually have to spend a week or more doing a SLAM so I wanted to try closing at SLAM level instead this year if it wouldn’t harm the gelcoat by doing this.
Is closing at SLAM level harmful on a fiberglass pool’s gelcoat?
- Thread starter schwim123
- Start date
SLAM is not harmful to people so it’s certainly not harmful to gelcoat. If the gel coat is failing, it’s just a matter of time.
The industry ignorantly ignores the science of the FC/CYA relationship. Your SLAM water has a lower active HOCL content than tap water. HOCL is the 'harsh' component responsible for bleaching and whatnot.
I've done both and the only year I got bit it was 70s in Jan/Feb. I believe I would have had a swamp either way with spring here for week at a time, several times. I should have checked my FC when it was so warm. Had I done so and replenished it, I wouldn't have had a swamp.
Close late, open early, check it mid season if it's freakishly warm.
When you got bit, had you used polyquat or chlorine at closing? It’s often in the 70s here for a week at a time after closing and it looks like it will be warmer than usual next week after it is closed. Does polyquat protect against algae better than chlorine if this happens? Is it possible to get enough chlorine in the pool without the pump running to ward off algae if we happen to get some 70 degree weather in the late fall or early winter and how do we mix it in without taking the cover off completely?
Polyquat is supposed to be a backup if you run out of chlorine. You can try it, but adding too much chlorine will degrade it. You can also just add some chlorine midway through the winter or early spring once the freeze risk has worn off. A couple days of 70 degrees isn’t going to do anything bad one way or another. It’s weeks of 70’s you have to pay attention to
Last edited:
If you're under the cover draining mid season, use the sump pump to circulate the water a bit and test for FC. It doesnt even matter if its a 6 or a 16. Its not 0, or close to it. You're already there with the cover open and maybe it saves you that one out of 10 years that you ran out of FC.
IMO there is no need for insurance (PQ) at this point. You're the insurance.
IMO there is no need for insurance (PQ) at this point. You're the insurance.