adjust cya before or after shocking

[Kateyru]

Hi,
I have an inground pool with SWG and vinyl liner. Since I live in Alabama, we don't really close our pool over the winter. We actually were in the pool in March My CYA is 30, and I have a little green algae which I really struggled to get rid of last summer and early fall. Not sure I got it all because it's in there now. My FC is 5, Ph is 7.6, and TA is 80. Should I get CYA to 70 before shocking with bleach to get rid of the algae or should I shock then add CYA?
Thanks so much. The website and forum have been extremely helpful.

[aylad]

Hi Kateyru, and welcome to the forum!!

I would shock with bleach to get rid of the algae, holding it at shock level until you are no longer lose any chlorine overnight (measuring it after sundown and again in the morning before the sun is on the pool). Once the algae is gone, then raise your CYA.

[BigDave]

I would go after the algae first and then raise the CYA after you're done, it should take less bleach to get to your shock level with a lower CYA. If dichlor shock is cheap in your area, you may consider using it to start your algae battle - it will add CYA as well as chlorine. Be sure to watch your CYA and pH if you do.

[Kateyru]

Will do, thanks!

[Kateyru]

Okay, I added dichlor last night. I tested ph this morning and it is way up...at least 8.2 (as high as my kit goes). I thought dichlor would lower the ph??? Should I add muriatic acid this morning?
Thanks.

[Watermom]

What is your chlorine level? If you test pH when they chlorine level is high, you can get false pH readings.

[Kateyru]

at least 10, it doesn't look much darker than that

[BigDave]

10? What are you using to measure chlorine? What kit? How much dichlor did you put in? Do you know how many gallons your pool is?

[Kateyru]

I am using Leslie Basic Poolcare OTO test kit (made by Taylor). I misread, chlorine is 5 but that's the highest on the kit. I added 37 oz. of dichlor. Pool is about 22,000 gallons. thanks!

[BigDave]

According to The Pool Calculator 37oz of dichlor will add 7ppm of FC and 6.4ppm CYA to your 22,000 gallon pool and drop the pH by 0.27. You may be able to use this dose of dichlor 4 or 5 more times before reaching your CYA goal.

I think you're going to need unstabilized chlorine - Bleach (Liquid Chlorine) or Cal-hypo to clean up. The pool is consuming chlorine too fast to reach and maintain shock level with just dichlor.

You'll also need Borax to raise pH after dichlor lowers it. I don't know why you get such a strange reading but dichlor should push pH down.

You'll also need "The Good Test Kit" the Taylor K-2006 (or K-2006C) available from the link in Watermom's Sig. It will let you eaisly measure the high chlorine levels you'll need (from Ben's Best Guess Chart) to finish off the algae in yourn pool.

Go ahead and add one more dose of dichlor if that's all you have on hand but don't use more without getting a reliable reading on your pH.