The urine that rays produce is pretty much pure ammonia, which eats away at your KH and GH since your PH is that high it should be pretty stable. So i would expect your PH to drop a little.
With a matured filter system, the KH will gradually goes down. NH3 --> NO2 -->NO3, during the process of converting NO2 to NO3 the by-product is Nitric acid that will react on your KH.