Money

This isnt a cheap past time.  Theres quite an investment to be made to get started, equipment can run into thousands, the fish themselves arent cheap and the food they do best on is expensive.

It will impact you electric and water bills if you're really that bothered too.  All in all things add up quickly and they change quickly too which usually means something else needs to be bought.  There also an addictive aspect to this where you will want a larger tank as soon as you've bought one and you'll always wish you had a large filter or a better light and on it goes.  You can find good second hand tanks and filter bargains if you look carefully but we careful and always remember that you are housing a large volume of water in your house.  So cheap, old rubber seals are not a great idea with several hundred litres of water running round them constantly for years on end.  Tanks can split and the bills will just get bigger.

One thing I have learnt is that there is a reason why the good stuff is expensive.  Most of the cheap equipment I have bought has either failed and caused more expense or not lasted as long as it should.  I've had a 20 quid heater over heat 5 40 quid fish.  Cheaper filters have leaked and connectors snapped.  Always get the best you can afford.  I have never seen cutting corners pay off in the long run.

Once you've got all the equipment needed there are some regular costs to consider, food is expensive and if you are getting things right they go through it very quickly.  Filter media needs regular changing and test kits need replacing and they do go out of date.  And all of this is needed to keep some very expensive fish alive.  And there it starts as once you get the bug you will always want more fish, which probably means another tank and it starts again.

TOP TIP - Some filter media is very expensive, sintered glass, ceramics tubes, bio this and that...  I read that 30 ppi foam is the best media for bacteria to colonise.  I've not proof but I have one filter full of it and its going well.  It was cheap too, no Ammonia or Nitrite in that tank, and it doesnt need cleaning that often either.