I use AqAdvisor
just as a guideline and comparing load of certain fish i might want to add.
For example not everything in that link is actually in the tank yet. The white skirt tetras and cherry red shrimp are not in but will be. the cherry reds I'm waiting for warmer weather to get shipped. The white skirt tetras will actually be glofish tetras that the kids want (Easter or summer birthday presents)
I used this to compare compatibility and bio load when adding other fish.
For example when I was looking at putting tiger bards in and got these warning.
Warning: Cherry Shrimp may become food for Tiger Barb.
Warning: Tiger Barb is too aggressive to co-exist with Neon Tetra.
Wanting some bigger fish for a "center piece" I was looking at Gourami I got basically the same warning for Blues Gourami but not Pearl Gourami.
It also gives good warnings about how many fish to keep together and other considerations like:
Note: Ruby Shark may jump - lids are recommended.
Warning: Ruby Shark needs to be kept alone.
Warning: At least 5 x Redline Shark are recommended in a group.
Now do I take those recommendations as law - NO but it does give me things to think about and consider.
I had to fudge my filter because I have a 55/75 which isn't and option only the Aqueon 55 is and the 55/75 has more the twice the flow. It also does not take into account sponge filters or under-gravel filters.
For my(wife's) 3 gal betta tank (I male betta, 1 oto and 3 ghost shrimp) this is what it tells me
Warning: Betta [Male] is not recommended for your tank - it may eventually outgrow your tank space, potentially reaching up to 2.3 inches.
Warning: Betta [Male] is not recommended to be with Ghost Shrimp - further research is highly recommended.
Warning: Oto is not recommended for your tank - it may eventually outgrow your tank space, potentially reaching up to 2 inches.
I don't believe any of that.
Again AqAdvisor is just one tool that can be useful in giving you things to consider but should not be the only tool you use or thought of as having hard fast laws in the reccomendations