High CL will not drop, high PH, calcium precipitate on pool bottom

[tomj]

For the last 3 years we had what I thought was problem with a DE filter leaking DE back into our in ground liner pool, powder on the bottom all the time & having to run our filter attached vac constantly. Replaced entire guts of hayward de4820 filter (grids and manifold, even though I was unable to find any defect) and eliminated the selector valve and installed a check valve between the pump and filter. Powder problem continued, so i was planning on switching to a cartridge filter after replacing our 12 year old liner this past fall. New liner installed, filled the pool got the water reasonably where it should be and then it was cold so didn't bother with much or any chlorine until opening a few weeks ago- ran the filter and no powder on the bottom, which was weird. Picked up an 80lb cal hypo bucket, added some and the powder was there the next morning. Now I KNOW this HAD to be calcium precipitate rather than DE; did some Googling and sometimes an issue with high PH & alk so got a pool water analysis from Ace Hardware:
FC 1.2ppm
TC 1.5oom
CC .3
PH 8.1
hardness 175
Alk w. stabilizer corr 91ppm
CYA 60ppm
copper .2[[m
Iron .1ppm

Added 1/2 gal muriatic and 2 gal liquid sodium hypochlorite & ran the pump for 2 days, no powder on the bottom since, so I may have the problem solved but I want to use cal hypo and am a little hesitant. My test kit (new reagents) sold by Ace shows PH now around 7.8. the CL on the test kit only goes to 3 but shows off the high side scale with even only one of the 5 drops used for the test- and the ace guys keep telling me to add that sodium hypo, which I did. I've not been back for another test at Ace, but looking for some help as to why my test kit is showing such high chlorine, why even if I skip a few days the test kit does not indicate that the chlorine concentration is coming down, and if I'll be OK and precipitate free using cal hypo with what my numbers would be now?

any help greatly appreciated
Tom

 

[JohnT]

Welcome to TFP!

I doubt it's calcium precipitate, but rather just un-dissolved cal hypo settling to the bottom of the pool. You normally want to dissolve the cal hypo in a bucket of water before adding it. Cal hypo can also cause cloudiness in the water and will eventually result in excess calcium in the water if you don't frequently replace water.

With your CYA at 60ppm, and with pool store testing the real number could be anywhere from 0 to 200ppm, you want your chlorine level at 7ppm anyway, so your chlorine may be low rather than high.

Take a look in Pool School for more information.

 

[tomj]

Thanks

I did dissolve the cal hypo in a bucket prior to adding it, then ran my filter driven polaris vac to clean up the powder. The powder reappeared the next afternoon. I then ran my polaris self powered vac with its own filter, and the powder was not in the bag when it was done, and again reappeared in smaller quantities the 3rd day. I lowered PH and now the powder is gone. I can only surmise that whatever was on the bottom either dissolved when the vac hit it or consisted of particles too small for the self powered vac to hold. I'm told what you see when you see undissolved cal hypo it is actually the calcium you see, the chlorine component dissolves almost immediately.

This is the first time in the 13 years that we have had our pool that the test kit I have does not indicate a drop in chlorine concentration when I don't add chlorine for a few days. The reading has been off the scale since opening, chlorine added or not. Note that we had a new liner installed just before we stopped using the pool last fall, I don't know if that has anything to do with it. new test kit with new reagents.

The water is only a few months old, cya buildup should be minimal because I used very little chem over the winter, just some tablets (maybe 15lbs since the pool was filled) in a floater and in the skimmer basket.

The Ace test said my CC is high...my test kit says high also although it only goes up to 3. I waited 5 DAYS & Just added 2 gal of sodium hypo today (29000 gal pool) & will see if there is any change either way in my readings tomorrow. I also feel that my chlorine is low, because of how little chlorine I've added so far this season but can't understand why I'm getting these high readings. can't see how no added chlorine in 5 days and see a hint of algae on the ladder but can still read off the scale on my ace kit, it would have read zero last year for sure, something is going on...
t