Salinity Question--Does Not Compute!

[Great Reefer Man]

Ok...here's the situation. I added 20gal of ro/di water to a plastic garbage can for mixing. I added 11, 3/4 cups of IO salt. A total of 9 and 1/4 cups. The directions on bag (and how Ive always done it!) say 1/2 cup per gallon. I always go over a little for a SG of about 1.025. Heres the different thing I did. I added about a quart of Kent brand phosphate sponge. The LFS where I get my water seems to have a little silicate problem since I always end up with diatoms. Since using phosphate sponge in my top off water and initially on the whole tank, I havent had a problem. I have not done a water change since using it so I have never mixed new salt while using the phosphate sponge at the same time.

Here is the problem. I took a SG reading of the batch of mixing water today and it was 1.014!!!!!! Its been mixing for about 20 hours! I used my swing arm hydrometer then double checked it with a glass floating one. I added two more cups of IO to the batch and my salinity is now 1.023.

What happened????? Where did all the salt go????? Was it absorbed somehow by the phospate sponge? Any ideas?

Dennis

[Penguin]

Eleven 3/4 cupfulls actually adds up to 8 and 1/4 cups, so you were 1 and 3/4 cups below the IO guideline. Adding 2 more cups brought you up to 10 and 1/4 total, and put your salinity pretty close to where you want to be. I don't know if the phosphate sponge could have had any effect but I doubt it.