Tank advice

[Essjay]

A 40 cm long tank will only take the smallest of fish. You say this is the tank you already have - I'm afraid to say it is far too small for your mollies. They need a tank at least 100cm long, preferably bigger.

Your water is just about soft enough for ember tetras http://www.seriouslyfish.com/species/hyphessobrycon-amandae/ and because the tank is 40 cm front to back, they should be OK.
Provided you put sand on the bottom of the tank, pygmy cories would work http://www.seriouslyfish.com/species/corydoras-pygmaeus/ These fish need to be in a group of at least 10.

10 of each of these fish would work in this tank if it had sand on the bottom rather than gravel. But I can't think of other fish that would also work. Endlers, for example, need harder water while fish in the Boraras genus eg chili rasboras need softer water (this is particularly important as Boraras tend to be wild caught and need water the same as where they originate)

 

[Darcy crook]

Looks like i have some improvements to make b cause i dont have sand either, ill list exactly what i have...
4 mollys
Two different types of tetra, 12 of each
Roughly 15 guppies
3 guarani
But again they don’t seem unhappy

 

[Essjay]

Your tank is very overstocked, and inappropriately stocked, I'm afraid.

Mollies need a much bigger tank, and much harder water. I don't know how long you've had them but they won't live their natural lifespan in 8 dH/140 ppm hardness.

What species are the gouramis? The only gouramis suitable for 55 litres are honey gouramis and possibly sparkling gouramis. Dwarf gouramis need at least 60cm swimming room and larger species need more than that.
What species are the tetras? Some tetras grow bigger and are faster swimming than others, but the vast majority need a tank longer than 40 cm.

The guppies should be OK. Your hardness is right at the bottom of their preferred range but commercially bred guppies can cope with wider ranges than wild guppies. They are also OK in a tank the size of yours. To be honest, 15 guppies in a 55 litre, 40cm cube tank (that's 14.5 gallons, and a 16 inch cube) makes it fully stocked without any other fish, particularly if you have males and females as they would make a lot more than 15 very quickly.


Gravel is fine for the substrate with these fish; it was in the possible new tank that you'd need sand if you want bottom dwellers - and the only bottom dwellers suitable for this tank are one of the dwarf cories, of which pygmy cories are the easiest to find in shops.

 

[Darcy crook]

I have diamond tetras and neon tetras, I’ve had my mollys for at least six months now and don’t seem any less active than the day i got them, the guarami i have are honey guarami so they’re suitable, so really my main problem are my mollys

 

[Essjay]

Both those tetras really need 60 cm swimming room,

The main problem, apart from the mollies, is that you have too many fish. 12 of just 1 species of tetra is fully stocked, on its own with no other fish. With 12 of 2 species, you are very overstocked. Then you need to add the gouramis, mollies and guppies.
Using an on-line calculator that is well known to be over-generous, you tank comes to 300% stocked, and another gives your stocking level at 266%. Even allowing for the fact that these stocking calculators are not terribly accurate, you are still very much overstocked.


If you were to get another tank the same size and move one of the tetras into that, keep the three gouramis with the neons, then rehome the mollies and guppies, both tanks would then each be fully stocked. And splitting the existing filter media between the two tanks, filling the gaps in the current filter with media from a new tank, would mean you wouldn't need to cycle the new one.


I know this is not what you want to hear, but it is the best solution for your fish.

 

[Darcy crook]

Thanks for the help im going to get this sorted

 

[Chief Brody]

You could do a tank of bottom feeders. A 20gallon long has a decent footprint so fish that stay out of the water column would be fine. Add a powerhead maybe and loaches or small cories would work. A pair of apistos would work. South american bumblebee cat would work. I love bottom feeders.

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[Essjay]

But not in the tanks in question, I'm afraid. They are cubes not long tanks, being 14.5 gallons volume with a footprint of 16 x 16 inches. This is the problem with cube tanks - small footprint for the volume, and not much swimming length.

 

[Chief Brody]

Ahh no litres not gallons I see... I'm americano

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[Essjay]

That's the only downside to having members from all over the world