Clear, but no chlorine???

[FormerBromineUser]

Just an aside here and sorry for hijacking you, MaryJo. BUT you are the man, BigDave for working so hard during Ben's hiatus. He is so incredible and we all owe him SO much. Thanks from me. Again, my apologies, MaryJo!

[mary jo]

Just checking in. Last night (Sunday) at 9pm I added the jugs of chlorine to get FC to 30. This morning at 7:30 I tested (using diluted sample as you described- 5:1, results x6 and DPD reagent) and got FC=18. My FAS reagent comes in today so I can get more accurate results.
I just added 3 jugs to get the FC back up to 30. My question is: how often do I check during the day?

[BigDave]

Check as soon as the FAS-DPD reagent comes in.

[FormerBromineUser]

Then, as often as you can to keep it at shock level. (Ignore purple highlighting).

[mary jo]

My reagent came in yesterday, and I tested throughout the day- tried to estimate testing times so that FC level never got below 25. Last night @ 11:00 the FC=33. this morning at 7:30 it was 22. Should I add more in the evening so that there is at least a 30FC level in the morning?

[CarlD]

You don't need to test and adjust your FC more than 3x day--Morning, mid-day, and after the sun passes in the evening. Morning and evening are the two most important tests.

Do we know your CYA/stabilizer level? If it's 100ppm or more, you need to maintain an FC level of 25 or more until the algae is completely dead.

Remember to run your filter 24/7, vacuum to waste, and brush the pool daily until you've won the battle.

[BigDave]

@CarlD:mary jo's pool has CYA of about 150ppm, CH of 750, a history of trichlor use, periods of zero measurable chlorine, and low pH. There's no visible algae, and high chlorine demand. The Nature 2 cartridge is in place but hasn't been replaced in the last two years. There is a possibility that some amount of fertilizer made it into the pool. My guesses are that some CYA may have been converted to ammonia causing chlorine demand (no bad smell so probably not); the fertilizer may be causing chlorine demand directly; or that a nascent algae bloom (possibly aided by fertilizer) is causing chlorine demand.

@mary jo:CarlD is right, three times during the day should be OK but I don't think you need to vac to waste since you can't see any algae.
Do you have CC readings for the FC tests last night and today?
I'd like to see the FC stay above 30 but we run the risk of bleaching the liner.
Please continue to measure FC and CC after the last dose in the eveing has had a chance to mix in and after the sun is down and again before the sun is on the pool and before adding more bleach.