Im a fraid not, the actual ballast is just for one bulb, if the bulbs smaller then it'll blow and if its to big then it'll blow the ballast.
Off the top of head i think the fishmate has the pls type, so its got two glass tubes and just two pins on one end.
In terms of new uv then look at either the tmc pondclear or the kockney koi UV filters, both of these go inline and if its the pressuised filter you got then it can go before or after the filter.