So, I can make space for another tank. I have a choice. I have space for a 70cm tank.

MTS has bitten hard, I know.

I have typical London tap, rock hard (pH 7.8, GH not far off Lake Malawi/Tanganyika levels, nitrates pretty high too sadly). I can't fit an RO or nitrate filter to the water supply, so anything that goes in the tank must like hard alkaline water.

Unfotunately they don't seem to exist, but I can either move the 60cm (24") 54L Korall I already have and I'll have space for another 30" (80cm-ish) to go next to the current one. Or I can keep the Korall where it is, get a 45x30x30 (18"x12"x12"), move the least killies over to the new tank, and rescape the current tank.

Either option is fairly do-able. All I'll need is a cheap clearseal, underlay, and a clip-on light. I already have filters, and can move media around to seed them as necessary.

Current stock across the tanks is:

54L A colony of Least Killies. Either to be kept in the 60L or moved to a smaller tank (if I go down that route).

70L 30"x12"x12" River tank with 2x Darters, 2x Gobies, 8x WCMMs.

390L ND 4x2x2 Odessa Barbs, American Flag Fish, Zebra Danios, Weather Loaches.

I love loaches, but most are too active or need it too soft and acidic for my water. I also love temperate species, but I'd like to try something new.

I'd like to have variety across the tanks, and I want to do this on the cheap, (hence buying a cheap clearseal box) so I don't really want to have to buy another external filter/powerhead for another river tank.

My thoughts are currently one of the following:

A trio/quartet of Paradise Fish (will need a 30"). Alternatively put the AFFs in the small tank and Paradise Fish in the big tank. That'd give me an "Asian" themed tank (with lots of distinctly non-asian plants) and two US Native tanks.

Tanganyikan Cichlids. Either put some Multies or a similar shell-dweller in the 60L, or get the 30" and get those and a pair of the small Juli species and have a community. The downside? What if they breed?!

Danio erythromicron (or however you spell it). Another "species only" densely planted tank, full of tiny fish which I'm sure will end up looking like the Least Killie set up with different tiny fish/shrimp.

Axolotls! One will need the 24" tank, two definitely the 30". But the room may get a little warm for them, especially in summer. I've also got no experience of amphibians.

So over to you. What would you do given my water and limitations. Go wild!

Oh my! I too would love to try Axolotls (the weird beasties they are lol) but I'd be tempted by shellies in that size set up.

Cathie here, often has babies that you can secure from her stock if you are near

Just down the road, so he knows he only has to say the word ... But they do breed a lot once settled ...

Its tempting, but so are Scarlet Badis (Dario dario), which I'd initially ignored, because I thought they were softwater- although this is apparently not true.

Lovely looking fish, those Badis. I'd go for them, personally.

Bumblebee gobies? Another species I can't have so I need someone else to do it!
http://www.seriouslyfish.com/species/brachygobius-doriae/

Dwarf puffers?
Though a harem of scarlet badis would be lovely