You're going to need a chlorine test that will give you results up to at least 20 ppm--look for a DPD-FAS chlorine test--uses a tablet or powder that goes into your water sample with drops you drop in and count. It's possible to do this with the smaller test block using a dilution method, but we'll be wildly guessing at accuracy, and since you're gonna need it later anyway, it's best to go ahead and get it now if you can. Knowing exact measurements will hel you get it cleared up much quicker.

Janet