PH

I have a 55 gallon tank with a wet/dry filter, emperor 280 and 400 on it. It had caribsea eco-complete planted as substrate, lots of driftwood and peat in the wet/dry filter along with phosguard. I change the tank water with R/O water that comes out with a PH of 5 but i buffer it up to 6 and as the week progresses the PH rises. The PH last week was a solid 6.2 but today it is about 7.5......what the heck and how the heck?

THANKS!!!!

so....i read the back of the products.....phosguard removes phosphates and all that good stuff.....the buffer im using is a phosphate buffer......wow......maybe i should read the labels.....

im not too sure about that....it is low range controller from KENT and it says it contains phosphate buffers.