Holy algae batman! New pool cover = problem opening.

[Backyardchemist]

Hi everyone,

We have an IGP, vinyl siding, @ 25000 gallons. We live in the northern US where winter means a solid freeze on the pool. For the past 7 years we have had a solid tarp as a pool cover (held down with water bags)which was great for keeping out leaves and awful to remove. After years of wrestling with it, and a few good sized tears, we decided to replace it with a mesh safety cover (the spring loaded kind that attaches to deck fasteners).

The good news was taking of the cover this spring was a piece of cake! Easy to remove, easy to clean and store. Also there were very few solids in the pool -- but holy algae batman! We had never seen the pool water so green.

We did our usual process of water balancing, super shock, and algaecide + 24/7 pool filter with daily filter cleanings, but we are still loosing significant chlorine ppm during the day. The odd thing is, we loose hardly any ppm over night. Here are the specifics:

At night we will add liquid chlorine. By morning, consistently numbers look like this:

FC=20-22
TA=70-80
PH=7.2-7.4
CYA=less than 20

By night time, TA, PH, & (of course) CYA remain the same but FC drops to 6-8 ppm. During the day we have the solar cover off and it has been blessedly sunny during the day. The pool is mostly clear but not entirely.

SO here's the question. I know CYA is low but I hesitate to add any in the event that organics are still consuming the chlorine. If my issue is one of organics, than I am worried about adding CYA because then I will have to up my chlorine and I am already burning through my supplies. OR, is the fact that I retain chlorine PPM overnight and losing it during the day indicative of a CYA problem.

Any thoughts you have would be greatly appreciated!

Sincerely,

Backyardchemist
25000, IGP, vinyl, chlorine.

 

[Richard320]

This year has been a big one for CYA breaking down into ammonia over the winter. You have the symptoms. Green pool, no CYA, voracious appetite for bleach. Somewhere here I read that the ratio is something like 10:1, such that 8 ppm ammonia will require 80 ppm bleach, separate from the bleach used killing algae and being lost to the sun!

Now your CYA is so low that the sun just destroys the chlorine before you get any algae-killing out of it.

If you can pass an official, exactly-by-the-instructions overnight loss test you've eradicated everything that's consuming your chlorine and you should boost your CYA level. If you can't, then you need to SLAM the pool.

 

[JasonLion]

As far as I can tell nothing is wrong. The overnight FC loss is the one that matters, and that says you are good. The amount of chlorine you lose during the day is a function of how high the FC level starts out. You are only losing a lot of chlorine because you start with a very high FC level. For that matter, CYA must be well above 20, or you would be losing way more chlorine than you are.

 

[Backyardchemist]

Humm ... so I am hearing two different things. From Richard, I'm hearing that I have too little CYA and from Jason I am hearing that I possibly have >20 CYA. Is it possible that my CYA reagent has gone bad and I'm getting a bad read? Also, I'm still loosing 14-16ppm of FC during the day. Would I loose more if I really had <20 CYA? It seems like I am loosing a lot.

For the record, I am using the TF-100 test kit.

I will make sure to do an exactly-by-the-instructions overnight loss test instead of my usual eyeball.

Thank you!

Backyardchemist

 

[Backyardchemist]

FYI ... just checked my CYA with my neighbor's TF-100 reagent and it is definitely below 20.

-Backyardchemist