Anybody have experience with the HTH metal control? I believe it is phosponic acid based rather than EDTA, similar to Jack's. I have used Jacks with good luck. Clears the iron I have in my pool right up when I add fill water. But...it's ~$25 a quart. I see amazon has HTH for 10 bucks a quart if you buy a 6 pack. Sounds too good to be true. I was going to try it out, but if anybody has a negative, or positive comment, I'd like to hear them.