Okay...alk at 200 is high, but in a vinyl pool it won't be a big deal unless you're using cal-hypo to chlorinate with and your calcium levels get too high.(that's what the cleaning granules are). When the calcium gets too high, you'll start seeing your water cloud when you add the chlorine. I would expect that to happen when your Calcium gets to 400 or so, but the number isn't the same from pool to pool. You can still use it for awhile, but at some point you're going to have to switch to bleach.

I don't understand what you mean by Cl at 1/2--do you mean .5 ppm? If so, you need to get some in the pool. Since your CYA black dot never went away, it means you have less than 20 ppm, and possibly none, in your pool (none is probably the case unless you've added some since you filled the pool). In that case, you need to add chlorine to approx. 3 ppm to keep your water clean--and don't let it get below 1. While you're at it, go ahead and add the label dose of CYA (the stabilizer) to get to 20 ppm. Don't broadcast it in the pool, though--either put it in the skimmer and don't backwash and retest for at least a week, or put it in a tube sock and put it in the skimmer or tied in front of a return. It still can take up to a week to completely dissolve, so don't add more for at least a week so you won't overshoot. Understand that when your CYA level increases, so must your Cl--see the "best guess" table in the chlorine forum.

I'll leave the filter question to somebody that knows more than me (CarlD!).

Janet