If you see the filter pressure rising, then the filter is doing its job in filtering out the dead algae. Remember, chlorine kills it, then the filter (or vac'ing to waste) removes it. However, you won't know if you've killed it all off until you can test chlorine after the sun is off the pool, and the next morning before the sun is on the pool, and lose less than 1 ppm of chlorine in the process. However, to do that, you are going to need drop-based testing--strips simply are not accurate or reliable enough to use for this purpose. Also, strips do a very, very poor job of measuring CYA--they can usually tell you if there is, or is not, CYA in the pool, but you need an accurate CYA level before I can begin to tell you where your chlorine level needs to be for shocking purposes,. The Best Guess table that Carl referenced above will explain that more fully, but in order to access it you need to log out to the main forum page, to go the "Using chlorine and chlorinating chemicals" subforum, then open the second sticky for the Best Guess Chart.