Hi, I have the pool calculator for the iPhone and I took my current readings and plugged them into the program. I have a salt level of 4100 and want to get it down to 3500. The program recommends I drain 15% of my pool water. I have no idea how much this is. What should I do?Base it on inches or what?

Clean out a Gallon Milk Jug. Fill it up with pool water. Go dump it down the toilet. Repeat about 1800 times.

sorry, I just left the jokes thread...

Why, that's exactly how I would do it.

No really though, you basically just need to drain off a little bit less than 1/4 of your water. If you pool is say, 8 feet in the deep end and 4 feet in the shallow end, then your average depth is 6 feet. 1/4 of that would be 1.5 feet. You would need to drain less than that. Basically, I would drain a foot of water off and refill and retest.

Unless your SWG is not generating chlorine and is giving you an error of "high salt", I wouldnt do anything. How did you measure your salt levels? Depending on how you measured, a lot of the tests and the reading you get on your SWG itself, will be off by some percentage. In most cases, an error of 300-500 ppm can be expected. Again, if your generator is making chlorine and is happy, the salt level will go down over time through splash out and rain dilution. If however, it is not operating due to high salt, you can figure out gallons per inch fairly easy.

You dont say how big your pool is and I see its a kidney shape so it might be a bit more difficult. But, the area of the pool multiplied by 0.083 (1/12/) gives you a volume in cubic feet. You can then calculate how many gallons of water is in that volume of pool.
For eample, my pool is 16 x 30. Thats roughly 480 sq ft give or take since its a kindney, but its close enough. Multiply that by 0.08 and that gives you 38.4 cubic feet. There are 7.43 gallons in a cubic foot, so 1 inch of water in a 480 sqft pool is equal to ~285 gallons. My pool is 14,000 gallon, so 17% would be 2380 gallons or about 8.5 inches of water.

Based on a prior bad experience, I'd have the salt level verified by a couple independent tests. I concur with bk 406 and not drain unless there is a good reason....