So I had a rena xp3 on my 30 gallon turtle/cichlid growout tank but now I have an eheim 2217 running on that tank with extra bio media. On my 240 gallon I have 1 rena xp4 and 1 rena xp3. I noticed that the tops for each filter is the same, only difference being the impellers.....So if I were to get a rena xp4 shell, impeller and another media basket, would that basically be an XP4 but with reduced pricing? Thanks, everyone!