Where'd the CYA go?

[usmarinemike]

White stuff is not iron or copper . . . unless you've added aluminum sulfate, it's probably calcium carbonate (edited - Pooldoc) from your cal hypo.

Aluminum Sulfate is typically used as flocculant, right? Didn't put any in, unless someone has discharged a fire extinguisher into my pool lately.

[usmarinemike]

Bucket test just stayed cloudy white. The pool finally went from green to blue last night. Here are my numbers this morning after testing with the K2006.

pH 7.3
TA 70ppm
CYA is just below 30. The dot disappeared with room for maybe a half a drop in the comparator before it overflowed.
FC=1.2 CC=1.2

Thing about the FC is that I put in almost 3 lbs of 73% cal-hypo last night. It certainly did it's job that time, but woah. I guess I'll be working down the chlorine demand every night for a while longer. At least it's finally blue and inviting.

What are the reasons/advantages/disadvantages to putting the cal-hypo directly into the skimmer?

[PoolDoc]

The disadvantage is that it's dangerous, if you don't make 100% certain that there are no OTHER chemicals it can encounter before reaching the filter.

The advantage is that you put the excess calcium on the filter, instead of the pool, and in the process, get improved filtration. If you do NOT do it this way, you'll tend to have problems with calcium build up, with scale and cloudiness resulting.

[usmarinemike]

Alright. Two nights in a row I've added enough chlorine to bring the pool up to the shock region on the BGC, and both nights the pool tested much, much lower 2 hours later. Tonight I started with .8ppm FC and added 3.5 gallons of 6%. I now have 2.0ppm. Lat night I added about 3lbs of 73% cal-hypo and 2 hours later it was around 2.0ppm. So two different Cl mediums show some wicked chlorine demand? To recap, the thread started with my missing 2.5 lbs of CYA. Does this sound close to the chlorine demand from ammonia? My pool went from clear green to clear blue last night, but I have a feeling that my adding a lot of the cal-hypo to the skimmer last night allowed my sand filter to finally hang on to whatever was in the water. What's going on?

[PoolDoc]

Two nights in a row I've added enough chlorine to bring the pool up to the shock region on the BGC, and both nights the pool tested much, much lower 2 hours later.

That's pretty definitive evidence that your pool had some CYA that got bio-degraded to ammonia or urea. But unless you want to take your water to a EPA certified lab, and have them do tests for COD (Chemical Oxygen Demand) and ammonia, we don't really have any idea how much ammonia is there, and consequently, we don't know how much chlorine it will take to clean up. We've seen it take 100+ gallons of household bleach on several occasions, when the CYA was very high the preceding fall.

But, knowing doesn't change anything: you're limited in how much chlorine you can prudently add at one time, both for the sake of your liner, and also to avoid the situation where you add a 50 ppm dose of FC when you only have 5 ppm of chlorine demand left!

By the way, keeping the pH on the high side of things, helps push the process toward less noxious intermediate products, as the chlorine breaks down the ammonia (or whatever is there in your pool).

[usmarinemike]

Working the pH up a little at a time. The owner used trichlor last season, and I assume every season because the floater was pretty beat up so the CYA was probably pretty high. I suppose 100 gallons isnt so bad. Great Value is about $1.50 this week. This will be one clean pool once the Cl holds.