Quick update.
Stats stayed stable in both tanks. I checked daily and I haven't had any spikes. There was a slight tint of nitrite in the 180 at one point (you know, when it turns a bit darker blue but not purple), but a water change brought that down again.
As I now know for sure that the 4fter, which was the 'holding tank', is going on Saturday to make space for the Vision 260, I have taken media of one of the internal filters (there are two) and split it between both tanks. I have now added many more fish to both tanks. In the 4fter remain the bottom dwellers, everyone else is transferred. I left them in for now, as the tank is 24 inch high and I need to empty out quite a bit of water first to be able to catch them without putting my face under water
Once the 4fter goes on Saturday I will put the Vision 260 in its place, transfer the bottom dwellers and the media of the other internal filter as it won't be needed anymore (I'm getting a mature, still running filter, for my Vision tank) which means that basically in one week I should have three fully running, cycled Juwel tanks
I know, I should have added mature media right from the beginning, yeah tell me off
Anyway, this is the current stocking:
Diego - 180
6 platies
1 swordtail
2 fem guppies
3 sailfin mollies
20 harlequin rasboras
Dora - 125
10 dwarf rainbows
2 dwarf gourami
8 neon tetras - I was tempted to give them away for free, but their colours look great under the high light, so will keep them
There are still cories and kuhlis and my two bristlenoses to transfer.
Will take pics and/or video later, but won't upload til tomorrow or so as it's bedtime soon.