Just noticed that one of the Guppy's is missing part of his tail, and is struggling to swim

[TacomaToker]

First issue...you have very soft water (this is the case along coastal Oregon, Washinghton and SW BC where I am). Species requiring harder water, such as all livebearers, cannot be healthy in our very soft water, so it would be a good idea to re-home the guppies. At the least, do not acquire any more livebearers (guppies, swordtails, platies, Endlers, mollies).

That brings us to the rainbowfish...some of these also require moderatel hard water, some are softer water. We will need to know the species; a photo of the fish will help if you don't know the name. Rainbowfish like tetras are shoaling fish, requiring a group, we can go into that when we know the species.

I see Colin posted as I have been typing, and he did not realize the soft water issue. Now he will.

I agree on the water changes; I change 60-70% of each of my tanks once each week.

Hey there, thanks for the answer. This tank is actually in northern CA, in the Bay Area. I should probably update my location. Is the water here hard or soft?

I attached a picture of my rainbow. I didn't take this pic, but it is almost exactly what they look like. I've got 3 of these guys, they don't seem to be unhappy but its hard to tell. Any info you can give is greatly appreciated, thank you!

Rainbow:

https://cdn11.bigcommerce.com/s-kkon4imfg5/images/stencil/1280x1280/products/170/434/RAINBOW_NEW_GUINEA_REGULAR__12710.1522374588.jpg?c=2

 

[Byron]

On the GH of your water, see if your water authority has a website, the data may be there. Or you can call them. Make sure you get the number and their unit of measure.

On the rainbowfish, the family Melanotaeniidae are not well known to me. @Colin_T will know right off.

 

[Colin_T]

the rainbowfish is Glossolepis incisus

the following link has all the current known rainbowfishes and might be of interest to you.

Melanotaeniidae and Pseudomugilidae

A website dedicated to Rainbowfishes of Australia and New Guinea

rainbowfish.angfaqld.org.au

 

[TacomaToker]

the rainbowfish is Glossolepis incisus

the following link has all the current known rainbowfishes and might be of interest to you.

Melanotaeniidae and Pseudomugilidae

A website dedicated to Rainbowfishes of Australia and New Guinea

rainbowfish.angfaqld.org.au

I've got 3 of these guys, they seem pretty relaxed most of the time. sometimes, they will chase each other around for a couple seconds. is this a point of concern or is it normal?

are they unhappy being in a group of 3 as opposed to a larger group?

 

[Byron]

I've got 3 of these guys, they seem pretty relaxed most of the time. sometimes, they will chase each other around for a couple seconds. is this a point of concern or is it normal?

are they unhappy being in a group of 3 as opposed to a larger group?

"Unhappy" may be difficult to define here. But three fish of a shoaling species like all rainbowfish need more than three to be healthy and relaxed, which may be better ways to think of it. With too few they are under stress, and this can increase from this or some other issues too, and this does impact how fish function. The shoaling instinct is programmed into their DNA, and they "expect" a group. The citation from the eminent aquarist Paul Loiselle in green in my signature block says it well.

 

[Colin_T]

It's pretty normal for rainbowfish but if you have 3 of them and they are all red in colour, they are all males. You could get 3 females to increase their numbers to 6 and that would make them happier. Females are bronze or silver in colour and have no red on them.

You have to watch the male G. incisus because big males can get aggressive to smaller fish. If there are a number of males in the tank they usually keep each other occupied, but sometimes one male will take over the tank and kick hell out of everything else in there. This is less of an issue if you have a group of them.