If you don't mind going for a bit of an expensive fertiliser, Seachem's Flourite is probably one of the best. It doesn't rot like some other fertilisers out there and it can also be mixed with dark coloured gravel which can produce a striking effect especially in a planted tank (since the flourite is redish). There are also new Seachem ground fertilisers that have recently come into many fish stores in New Zealand. The JBL aquabasis (I think it's called that..can't remember..) isn't bad either. If you are planning on keeping many types of fine leaved plants, e.g. Hairgrass, I would personally recommend it. Good luck.