Cloudy water...then very small amount of algae...then algae bloom

Help...I'm 100% stumped.

I don't understand why my pool became cloudy and why I have an algae bloom with high FAC.

Vinyl/18,000 gal
Sand filter

Most recent readings:
FAC: 5.0
TAC: 5.0
CH: 30
CYA: 30
TA: 110
PH: 7.6

About 10 days ago I shocked the pool with dichlor. About 2 days later I first noticed some cloudiness (non-algae to my eye). I tested via strips and saw that my FAC/TAC were both over 10+; I thought it was odd but made no changes. The next day I tested via strip and was surprised that the FAC had not dropped and also noticed a little algae-thought that was very odd.

Started testing every day with strips and/or drops. The thing that struck me as very odd was that the FAC was dropping much slower than normal-and the algae continued to worsen even with unswimmable and very high FAC and I now had the start of a full-fledged algae bloom.

I looked through the poolsolutions.com article: 100 reasons for a cloudy pool and nothing jumped out other than sand in the pool from sand filter (I changed from sand to zeosand about two months ago...a little cloudiness at first then cleared in a few days).

I went to Leslie's Pools and had them test the water to confirm my numbers; their results were very similar to mine. The guy told me my cloudy water was caused by low calcium hardness and I walked out of the store with 25 lbs. of Calcium Hardness Plus; I have not added this to the pool yet since I reached the probably uneducated conclusion that the cloudiness was not caused by low CH.

As a stab in the dark-its been very hot and sunny here in Atlanta for the last month and the water is very warm; even at the bottom of the pool (9 feet deep) its 84 degrees. Another stab in the dark-I've had algae blooms before and they usually "blow-up" in a very short time: 24-48 hours; and my FAC had reached .5 or less. This algae bloom (even with very high FAC) has been almost in slow motion.

Any help would be greatly appreciated.

Thanks.

Hi, and welcome!! Odds are that the bloom went in slow motion because you had enough chlorine to slow it down but not stop it. You need to shock the pool up to 15 ppm and keep it there by testing and adding more chlorine as often as possible, filter running 24/7, brushing the pool daily. The pool willcleqr if you keep the chlorine up. I can assure you the cloudiness was NOT due to low calcium.

Forget to add one thing:

Prior to shocking with dichlor 10 days ago the water was perfectly clear...pretty normal readings except PH was a little low.

Thanks for the replies thus far; I'll return the Calcium Hardness Plus for a RC submarine; it will probably last a week with the kids and the occasional dog.