CYA Low 90/100 Yeah I Said Low! Now My FC Is Going Bye Bye...

during the time isaac blew through the carribbean and gulf of mexico we were getting a lot of on and off heavy rains. on monday 8/27/12 we had a heavy rain band that stayed over our area for several hours causing a lot of flooding. i must have drained 1ft of water of my pool in just a couple of days.

due to all the rain there was a couple days that i was unable to test FC as i felt i would not get accurate numbers as the water was being diluted constantly by steady rain. i did however bump up my FC ( before teh storm ) and added 2-3 quarts of bleach a day to help deal with all the rain.

well the rains stopped and i was finally able to test ( in my garage late on 8/27 ) after adding 1.4 gal of bleach a few hours before. i measured 20ppm FC so im guessing i was right around 8ppm FC before adding the 1.4 gal.... im not supposed to go below 8 with my CYA of 110/120... so i just bumped my FC up and thought every thing was peachy!

because of all the flooding i was getting home after dark due to an increase in my work load, so on 9-1-12 i was finally able to run a full set of test's. here are the numbers.

FC - 9ppm ( i expected more FC )
CC - 0 ( i always get a CC of 0 )
PH - 7.6 ( been holding 7.6 all sumer )
TA - 90/100 ( was at 120 most of the summer and holding )
CYA - 90/100 ( was running 110/120 all summer and i like it like that! )

the last few days of testing ive seen in increase in FC loss. i tested on 9-1-12 in the evening at 7:45 pm ( sun was off the pool ) and measured again on 9-2-12 in the morning at 7:30am ( before sun was on the pool ) and lost 2.5ppm overnight. im used to losing only 2-3ppm in 24 hours!

this evening i measured a trace of CC but there was no CC during this whole isaac thing. i did vacume out a bunch of leaves, bugs, pine needles, etc yesterday...i didnt see any visable algae during vacuming as i use a mask and snorkle so i can see what im doing.

i tested FC tonight ( and got the trace of CC ) so im gonna measure again in the morning. if i lose more than 1ppm of FC im going to start the shocking process up to 25ppm. im also going to drop a couple of triclor pucks in the floatie to get back some CYA....

i dont think the FC lose if from the drop in CYA/UV but im no expert! any other thoughts or ideas? the pool is crystal clear by the way.

Sounds like it could be the beginning of something trying to grow in your pool. Has your bather load been light or heavy? With a loss of 2.5 overnight, I'd say there has to be something in the water that the chlorine is attempting to "eat" thereby causing the loss you are seeing. If your CYA readings are accurate you need to keep the CL levels between 20-25 until you have a CL loss of less than 1ppm overnight. I'd keep it up an extra day just for good measure.

My guess is that the rains and wind washed some stuff into the pool and increased your chlorine demand. You also had some time when the FC was low because of the rain and the inability to chlorinate which can allow something to take hold, Most likely it's a nascent algae bloom or some extra organic matter in the water. The fact that there is a bit of CC is a good indicator, even if the water is clear.

This is pretty common here in Florida during our 'wet' season. (Florida only has two seasons, wet and dry! Most people don't realize that the Everglades is considered to be desert in winter because it loses more water than it gets in precipitation.)
Don't lose any sleep over it and just shock the pool to correct the problem. What you describe is fairly normal.

I agree with Waterbear--hurricane-driven rains always carry a load of "goo" with them, for some reason, so I always shock the pool after we've had one come through...

Plus, all that organic debris in there (leaves, twigs, dirt, etc.) also causes you to use more chlorine.

ok... looking back at my pool log i vacumed all the debris and goo out of the pool on 9-3-12 about mid day ( finally had the time ) and also cleaned out the filter which was pretty dirty. i then measured FC that night ( 6:30pm ) and got 13.5PPM i then added 3 qtrs of bleach which should have bumped me up to around 19.5PPM. i measured again on 9-4-12 at 7:00pm and got 13PPM which was a loss of 6.5PPM in just over 24hours.

i tested this morning at 7:45am and got 12.5PPM, so i only had a .5PPM loss last night. after this test i added one trichlor puck in the floatie to get some of my CYA back, and add some FC. i just tested and had 12.5PPM FC and 0 CC, so it seems it may have just been a matter of getting all the debris and goo out of the filter and hitting the pool with a nice dose of bleach after the clean up.

just for good measure i just dosed with 7 qtrs of bleach which should get me up to around 26.5PPM. now i need to run out and get some more bleach since i only have about 1 qrt left...lol

im confident my CYA test the other day was accurate, so ill measure again after the trichlor puck has disolved and add another if needed to get me back to my " sweet spot "

funny thing is none of our rainy/windy summer storms have caused me such a chlorine demand, even when it was blowing debris into the pool. must be something special with hurricane storms.

thanks for the input guys and gals!