Tetra CO2 test kits & DIY phosphate removal

Does anyone have any experience with Tetra's CO2 test kit? I just got one
today and tested the CO2 levels in my 55 gal tank. To my suprise, it
indicated that the CO2 level in the water was too high. I use a
canister-regulator-needle valve setup, with airline tubing directing the CO2
flow into an Aquaclear 201 powerhead, which just shoots the bubbles out into
the tank. There is no reactor involved. The tank is covered by glass
canopies, which don't allow for much air to get in or escape, and the system
runs 24 hours a day, which perhaps is the explanation. Still, the Tetra kit
said if the CO2 level was "too high"  (somewhere above 15mg per liter) it
could cause problems with the fish.  My fish (including a betta) seem to be
fine, however. Plus which I still have some algae problems. The kit also does
not give exact measurements, just a two color reference chart which tells you
if the CO2 levels are too low (less than 2.5mg/l), within the appropriate
range (2.5-15mg/l) or too high (more than 15mg/l). Does anybody else use
Tetras' kit or have any thoughts on this?

Also, I was wondering if there are any DIY phosphate removal substances or
such things. I remember reading in the past that some people were
experimenting in that area. Was anyone succesfull? Or does anybody know of a
cheap commercial alternative? The phopshate removal products that I have seen
in stores and catalogs are all pretty expensive and exhaust themselves

                                           Thanks for any help,

                                                         Matt MacGregor