CYA all gone. Algae high. Wife mad.

Hawk Stone

Member
Jun 8, 2015
6
Boise/ID
Hello everyone. As always, I'm grateful for this forum. I have an unusual situation, and I'd like a little advice.
Background... I was heading out of town, and didn't have any bleach. So I crushed up about 10 trichlor tabs and put them in a floating dispenser. (I know, I know...)

When I came back, the pool was thick with algae. FC, CC and CYA were zero. The crushed up tabs were dissolved.
I added eight gallons of 12.5% chlorine, and nothing changed. That was last week, and the algae has just gotten worse.

FC, CC and CYA are still zero, pH is high (>8.2). Ammonia is 0.5ppm.
In the past, the 40,000gal pool has gone from 80 CYA to zero over the winter. I think the same thing probably happened here, and all that chlorine went to breaking the ammonia, leaving none to kill the algae. If so, the solution would be... more chlorine (isn't it always?).

Finally, it's probably unrelated, but my tabs all got wet this spring. I dried them out, but I have to approach the bucket with my eyes and mouth closed now because of the fumes.

My questions:
1. Did I diagnose the problem correctly?
2. How do I avoid having to deal with all my CYA turning into ammonia every year?
3. I have 'free' refill water - a super-low-nutrient canal. I have not significantly replaced the water in the pool for 6 years, when I replaced a quarter of it. Might it be worth just starting over?

Thanks for your help
Hawk
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
10,794
Northern NJ
With ammonia your ph is low and your CC is high. You don’t show all the symptoms of ammonia. You do show the symptoms of a major algae bloom consuming your chlorine.

Pour 10 ppm of chlorine into your water and check your FC and CC after 10 minutes and report back.

If your second question is when you open your pool in the spring, then you need to close your pool when water temp is below 60 and add Polyquat 60 at closing. Open the pool early.

Finally, if you can safely do a drain and refill it may help but you will still need to do the SLAM Process.
 
Last edited:

Hawk Stone

Member
Jun 8, 2015
6
Boise/ID
No fertilizer use for years.
Is it possible that the tabs getting wet could have somehow destroyed their CYA content? If not, is it safe to assume the CYA was bacterially converted to ammonia?
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
10,794
Northern NJ
Your ammonia test only showed 0.5. It takes 10 ppm of CL to clear 1 ppm of ammonia. It would have taken only 5 ppm of chlorine to clear what you tested.

You don’t have all the indications of ammonia.

Did you do the 10 ppm 10 minute test?
 

Hawk Stone

Member
Jun 8, 2015
6
Boise/ID
Updated information...
I went to backwash the filter, which had been acting strangely anyway. No slurry came out, just clear water. Turns out there was no DE. Last time I backwashed, I think I accidentally recharged the filter with 5.3lbs of probably soda ash.

That would explain the high pH and persistent algae, no?

I'm going to wait for nightfall, then slam the pool.
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
22,449
Laughlin, NV
You should take the grids out and clean them. Running them without DE normally can make them unusable as dirt/other stuff clogs them.

Soda ash would raise TA and pH. FC prevents algae.
 

Hawk Stone

Member
Jun 8, 2015
6
Boise/ID
Thanks for the help.
The pool is back to normal now. I had indeed put soda ash instead of DE in the filter.
The overnight loss test, and the 10 minute test told me what the problem was.
SLAM, acid, and finally... no more algae.

Follow-up question... I think my grids are starting to fail on my DE filter. Specifically, there's a significant puff of DE into the pool when I backwash, indicating a possible hole in the filter grid. Can that be fixed with some silicone, or is it time to just replace the grids?

Hawk