any help appreciated....

[mspool]

fiberglass 27,000 g pool. and live in the deep south. I used only bleach last summer, but decided to use my chlorinator with pucks for the winter. I vacuumed this morning and noticed pool slightly green. took my numbers and had 0 cl. My pucks must have run out. anyway added a lot of bleach and pool already looks better. So guess I will get back to slugging in the bleach every day, but enjoyed my vacation from bleach by using the chlorinator. I decided to test my cya level just curious how high it would be by using the pucks all winter. Much to my surprise my cya level is below 20. Now I think I need to add something to bring it up. Not sure what to do here and have no idea why my cya level did not rise. Does anyone have any suggestions or opinions on this matter.

[CrisL]

If you still have pucks, I would contiue to use them and turn the chlorinator up. Test the cya every week or so and when you hit 40 or so, switch to bleach. The cya sometimes gets eaten in pools that develop algae problems. There is some technical discussion as to why this happens on other threads, but it is beyond what I understand with my limited knowledge.

[chem geek]

Your CYA of 20 isn't terribly low so I would just continue to use Trichlor pucks for a short while until you get to around 30 ppm CYA. During the winter, chlorine use is very, very low due to the cold water temperatures. One 3" 8-ounce puck of Trichlor will add 2 ppm FC to your pool and 1.2 ppm of CYA and I'll bet that you didn't add much more than 20 pucks over your winter, right? That would explain your relatively low CYA level -- of course, I don't know what CYA level you started with.

If you had winter rains, then your pool may have overflowed with rain water and that would have diluted everything in your pool, including CYA.

Also, several users have reported drops in CYA over the winter. If your chlorine went to zero, then there are anaerobic bacteria that actually consume CYA as food -- they are normally found in soil but can find their way into your pool. So that could have happened as well. Some users even report CYA drops over the winter even with FC that didn't go to zero, but that's still a mystery to me.

Richard