Well thankyou for that very informative answer it is clear I haven't put enough thought into this. The aquarium shop is closed tomorrow so i shall return platys on Monday morning. So in regards to neons do you have any advice on suitable tankmates ?
You are most welcome.
Assuming this is the 60 liter (15 gallon) tank mentioned initially, I would first increase the group of neon tetra. Except...to comment on your previous remark on the hardiness of this species today, yes this is true--this fish has been commercially bred for decades and for various reasons it has weakened through this compared to wild caught fish of the same species. So at this point, knowing your water parameters now, you have another option and that is to acquire the closely-related but somewhat stronger species cardinal tetra,
Paracheirodon axelrodi. This species will shoal with its close cousins,
P. innesi (neon). There is also a third,
P. simulans, the false neon or green neon; this species is actually closer to the cardinal than either are to the neon, in its DNA, but they are still clearly evolved from the same ancestor so they are all very close. [My friend Heiko Bleher discovered a fourth "neon" species in 2005 but it has not beeen imported so far as I know; it is more closely related to the neon tetra in DNA.] The P. simulans (false or green neon) is a sensitive species, and will always be wild caught. The cardinal tetra is a bit more adaptable though like all characins (tetras, hatchets, pencilfish) not particularly "robust." This family of fish, characidae, is sensitive to water parameters, water conditions, and all chemicals. I don't want to scare you, just trying to point out the facts.
So, back to the neons, you could get more, at least another 4-5, for a group of 8-9 total. Or you could choose cardinal tetra, in a group of minimum five. They will as I say shoal together so the "shoaling" need is met, and in time if the neons should die off you could acquire more cardinals and end up with just cardinals.
Still wiith the 60 liter tank, with the additional 5-6 neons or cardinals...how about some substrate level cories? The "dwarf" species particularly (
Corydoras pygmaeus,
C. habrosus) would be ideally suited here. You do need sand for the substrate though. We can discuss more if interested. For the upper level, there are hatchetfish provided they are the smaller species in
Carnegiella. The marble hatchetfish,
Carnegiella strigata, is frequently seen in the hobby. A group of 7-8 would work.
Before you go down any of these roads, we should consider the aquascape, as these fish have some needs and expectations. Do you have or do you intend to have any live plants? This is fine either way, to be authentic, but it is an important part of the biological system so worth knowing. For the decor, lots of wood, as branches, logs, standing tree trunks. Dried leaves collected from a safe site can bee used for more authenticity. I'm tossing out ideas here, we can detail later.