I am setting up a new 6ft tank and am currently cycling it and getting ready to move my current fish from the 2.5ft tank to the 6ft.
Great, it's definitely a step up from a 2.5 ft. Why did you decide to properly cycle instead of moving over the filter media into the new filter?
There are so many fish to choose from to populate my tank, and I want to make sure I do it right.
That's what we like to hear
Ouch, ouch, ouch! I'll go through them one by one for you…
* 1 molly - apart from balloon mollies being one of the more warped fish, they are also social fish, so benefit from others of their own kind; I generally recommend 5+ fish of one sex, unless you want to breed them, in which case at least 2 females per male; might be "too fragile" to mix with some of the other stock; hardwater fish
* 3 dwarf gourami - really need good quality water; are they 1m 2f?; neutral water fish
* 4 bala (silver) sharks - schooling, keep 6+, and ideally 10+; 6 ft tank is not big enough, I've seen them stunted in a much larger tank (ca. 8*3*4 ft), not compatible with the smaller fish, really; soft-neutral water fish
* 1 three spot gourami - I really don't like keeping fish on their own unless they're solitary, not very nice for them; a 6 ft tank will take up to 1-2m 3-5f; neutral water fish
* 2 clown loach - schooling fish, keep in groups of at least 6+, and ideally 10+; sometimes don't take to late introductions, so add new fish *when* moving to new tank; should have lots of caves; ideally should have an over 6 ft tank, but a 6 ft is a good start as they're slow growers; soft-neutral water fish
* 2 pictus catfish - eat small fish like balloon mollies and dwarf gouramis; shoaling species, keep 6+; bothers slow fish at night (clown loaches and gouramis) so not really compatible with them
In other words, I would actually leave the molly and the dwarf gouramis in the 2.5 ft tank and move the rest up, with a view to finding the pictus (or the three spot gourami and the clown loaches) a new home. Some of the fish you have there will live for a very long time, so you're really looking at having the tank with the same stock for 20-25+ years, unless you will be willing to part with them.
I was thinking of getting a couple of schools of Danios (Zebras & Glowlights x 10 ea) as the schooling fish, 6 glass catfish, 2 additional clown loach and 1 more pictus (a friend needs a home for hers).
Danios will become pictus dinner, glass cats are not suitable for a tank which is that active (they will hide and die), the clowns and pictus need to be in larger groups still.
Schooling and shoaling species (like danios, tetras, barbs, rasboras, loaches, corys,
etc.) must be kept in groups of at least 6 and ideally in groups of 10-15+. There are even some species which in practice should only be kept in groups of 10+. This is because in the wild, they live in groups of a few hundres to tens of thousands, and without these groups, they do not have the confidence that they need, and sometimes they even end up behaving quite oddly compared to how they should.
Come back to us with your thoughts on the above and we can work on a stocking list. Also, what are the other two dimensions of the new tank? For the moment, I am thinking something along the lines of:
* 2m 4f
Trichopodus trichopterus of various colours
* 10-15 clown loaches
* 25 larger schooling fish of one species (danios, barbs, rasboras or similar)