Look at it like this. If you pour a cup of polutant into a 6g tank you have a disaster. If you pour the same amount into a 40g tank, not so bad. Also smaller tanks are more subject to changes in the surounding ambient temperature.

The flip side is that the initial investment goes up along with the number of gallons.

I like to recomend a 40g breeder as a starter. Not too big or too small, good size for aquascaping, will allow you to keep several fishes, lots of surface area for gas exchange and not too deep (if you decide to add corals later, deep tanks are expensive to light). If you add a small sump to this, you really have a good sized system.

So many species, so little money!

I would recommend starting maybe with a little bigger than that, such as 20 or 15 gallons.

Three years Saltwater

Two weeks FW

24 gal SW Reef

10 gal FW Planted

*In the making 180 gal Shark/Ray tank*