I've been buying RO/DI from a LFS, and mixing Tunze salt in a 32gal trash can every week. I let the water circulate with a Rio1300 (I think) and a 300W heater. Once the water is right I turn off the heater and through out the week change about 20 gallons. Today I noticed that the fresh salt water was a little yellow, and the trash can looked to have brown crust on the sides and bottom. Is this precip? I've never noticed it until today when I was going to use the last bit of water, and get ready to make a new batch for the following week. I also have 25 gallons of RO/DI on hand in 7 gallon buckets sitting for about a week as I'm on a cycle. My big question is, this ok? Or does the water quality decline rapidly, as the fresh sits undisturbed for about 5-6 days, and the salt water sits in the can circulating with the Rio pump? I through out the remaining water as I'll buy fresh stuff tomorrow, I didn't want to risk it.