Hex tanks are nice shapes, but I haven't found any that I find personally appealing. Here are some of the arguments against hex tanks, especially the taller varieties.
1) Height
a) Only the top inch or so of water in a fish tank is truely fresh water that recieves gas exchange with the atmosphere. Every layer of water underneath requires good filtration/circulation to keep it fresh and well oxygenated. Most HOB filters cannot reach the depth necessary to draw rotten water off the bottom of the tank, causing stagnation of the lower levels of the water. This can be toxic to bottom dwelling fish and if left untreated will eventually kill the entire tank. Most circulation problems inherant in a hex tank can be solved by getting a good (costly) canister filter 2X the recommended rate, or by placing airstone bubblers strategically along the bottom. Most fish are frightened by airstones, and some people don't find these aestically pleasing.
b) Cleaning. Hex tanks can be a b*tch to reach down onto the bottom of to clean and gravel vac properly.
2) Surface area
a) Again, this has to do with gas exhange of the atmostphere, the less surface area a tank has the less gas exhange, the less fish you can keep.
b) Most surface fish such as danios, rainbows, gorumais, require more surface space than other fish and would not be happy in a hex
3) Narrowness
a) Again, most fish, especially your streamlined fast swimmers such as rainbows, barbs, bala sharks etc will be constantly racing into the walls and not have enough room to properly swim around. Most fish would like a long tank to establish territories in so they don't have to be right on top of their neighbors.
b) It can be really hard to purchase equipment to fit the odd shape of a hex. Most standard stuff is made for rectangles.
c) I find the hex shape kinda distorts the fish and gives me less of a viewing field than I like.
4) Stocking levels. I've always been told only place 1/2 the amount of fish into a hex as would fit into the same gallonage cube-based tank. This is again because of filtration difficulties and territorial imperatives.
Some pro's to hex tanks:
1) They fit nearly anywhere you have a small space for.
That's all I can think of.
~~Colesea
