^^Ammonia, nitrite and nitrate are the absolutely essential ones. A ph test would also be advisable. The brand Hagen do some decent enough test kits, individual ones - which are more than ok, or whole case kits which might prove expensive, though it depends on how many tests they carry. I'd just buy the above individually, but check out your local fish store for any deals that might be going, you might be able to save a good few quid.
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