Quote Originally Posted by btozzo View Post
1. Free Chlorine 1.6 ppm
2. Combined Chlorine 0.4 ppm
3. pH 7.4
4. Alkalinity 180
5. CYA < 30 ( I could see the black dot when it was completely full!)
6. Calcium Hardness 220
16 x 36 24000 vinyl in-ground with Hayward EC 65, 1 skimmer and 3 returns

My first questions is that I am backwashing and adding DE and my circulation is slowing down and pressure up to about 24 pretty quickly. When I backwash my pressure drops to around 12. Can this be due to my CYA? I seem to remember something about that in the Taylor book.

Second, I believe my CYA and my alkalinity are connected. How much of what should I add to get my CYA up a little?
In your last thread you mentioned having a bunch of "rap" at the bottom of your pool; are you still cleaning that up/perhaps that's affecting your filter pressure? With your level, CYA would have nothing to do with it (I don't think it would at any reasonable level).

CYA and TA aren't connected, it's pH & TA that are. If you up your CYA between 30 & 50 you'll see less chlorine loss everyday. Some people keep it higher due to sun/heat, but then you have to keep your chlorine levels up (see the Best Guess CYA chart). Be careful adding CYA, it takes a few days/week to show up on a test after adding it.