I need help bad.... This is my first year owning a pool and I am so lost... I have a 15FT Metal frame Intex pool with the skimmer attached to the side. I have had it up for about a week and the water has stayed clean til now. I went out this morning to turn the pump on and saw a brown like dust all on the bottom. The ph level is good but the chlorine level isn't even showing up, But I do keep 2 1 inch tabs in the filter and they do dissolve. I clean the filter daily and this morning I noticed the brown dusting all over the filter itself. Now here is probably my biggest problem.. I do not cover the pool at night or when it rains, Is that what I am doing wrong or is there a miracle chemical I can add to it? Like I said before I am so lost and do not want to have to drain it cause it is a 4000 gallon pool... Please help!!!!