Stocking ideas - 54L

[Fishtank]

Hi, I have recently bought a 54L quarantine tank... and have the urge to stock it as a full time tank
I think I would really like a beta fish and hearing from other people they are better kept alone. Could I have a beta fish and some snails? Or some other minimal stocking perhaps?

I am not in a rush for this one, those of you who may have seen my other threads (PH, KH, GH - sorry in advance & quarantining fish - medication) may be aware that I have been struggling with my KH and this has caused me some lost fish the last few days, I have now added crushed coral and have kept my dKH at 4 most of the day - wish me luck! I also want to assure everyone I will NOT be getting any more fish until everything is settled again. I am simply keen to research and try to do my best with any fish I have/get in the future

Water parameters are PH - 7.2/ KH - 2/ GH - 3/. I fishless cycle my tanks before adding extra stock anywhere and use liquid test kits. My main DP due to stocking doesn't experience many swings at all, so that hasn't been a concern (main is 180 litres and is relatively lightly stocked right now). My problems have been with the small quarantine tanks (54L, 25L and 30L?) very small, usually used for quarantine or hospital setups but as stated above, I have added crushed coral to try and combat this and have other stuff on hand in case things go South.

[plankton]

If you want to keep snails in soft water you'll need to add calcium so their shells don't go soft.
Cheapest (and I always recommend this anyway) is to get a cuttlefish "bone" (as used in budgie cages), break a small piece off, boil it for a couple of minutes and drop it in the tank, they will rasp on it for the calcium.
When it runs out, do the same again. The "bone" will last ages.....

[Fishtank]

Thanks! Will that alter kh? I was going to put crushed coral but maybe just cuttlefish in that tank instead?

[plankton]

It won't have much effect, if any.