You can get rubble pretty cheap at the pet store on stellhorn and maplecrest.
The mont will love that 10k. It has blown up under mine, my problem was not having any other lighting to speak of and I lost the color pop in the 10k, but when the MH went off for the night and my actinic was one, it glows red.
I have never heard of a good test kit for phospates. For the money of the test kit on that I would just by a phosban reactor and media, then you should not have to worry about it at all.