Stocking My Tank

When you say the tank will sortly be ready for stocking - have you done a fish less cycle with ammonia? If so you can stock all fish in one go. If you haven’t got the nitrogen cycle set up then you ideally shouldn’t stock with fish yet. Unless you have a healthy amount of plant growth? If you can let use know how you have prepared you tank we will be able to advise appropriate next steps...

Otherwise your overall stocking plans sound a tad much for the size of tank you have:
6x 3cm Cardinals @ 18cm
6x 4cm Penguin tetra @ 24cm
6x 3cm Panda Cory @ 18cm
= 60cm stocking of max 57cm (though I wouldn’t go over 50 of fish fully grown)

I would advise choosing a smaller black and white species over the penguin tetra - perhaps the black neon tetra - or for a more contrasting body shape the black phantom tetra. This will bring you back within a reasonable stocking level for your tank. I would probably personally drop the number of corys to four as I don’t find they need to be in such large groups (though others might disagree with me here).

Hi Thanks for reply.
Yes I have cycled the tank.
You had me down for 6 Pander Corys I only listed 3. Heard various reports they are ok in 3s or 6 and above but not a pair or single.
6 cardinal Tetra      18cm
6 penguin  Tetra     24cm
3 Pander Cory          9cm

My daughter also wants a Striped Snail lol

All = 51cm

The only options I can think of for a tank of your dimensions, and which match your water hardness, are a betta or dwarf puffer fish. Even taking into account you using reverse-osmosis water to soften your water, I can't think of any more. There are a few options for tanks with a footprint of 45x30cm minimum (eg celestial pearl danios, ember tetra, bororas brigittae) but many more for 60x30cm minimum footprint.

I would really urge you to look at the species profiles and their requirements on https://www.seriouslyfish.com/knowledge-base/ which is more up-to-date and a more comprehensive source than our own Fish Profiles on here - they detail the minimum requirements for fish, including tank size, shoal size, etc. As fishkeepers, we have a responsibility for ensuring that we do the research beforehand to ensure the welfare of the fish we own, as any pet owner does.

Nerite snails are lovely - zebra snails are stripy and would be fine in your existing tank.

For the fish you suggest, it sounds like a second tank for them is the best plan - if you've cycled the filter as per Matt's query, you can easily transfer it (or at least its filter media) into it and it will be instantly cycled.

I stopped using the water from shop as they were always out so went straight back to tap water before guppies were introduced.
It seems stable now between 7 and 10 according to the strips. The Api kit does not test for Hardness only PH High PH nitrate nitrite and Ammonia.
I think it was the hardscape and wood that might have made it high to start with. Tap water tested is same 7 to 10 on strips.