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[Spalders]

My tank now has 12 Columbian tetras and some Cherry Barbs. Problem is that all the fish are staying near the substrate or mainly in the lower quarter of the tank (unless being fed of course.)

I would like something to liven up the middle to top area. Having hard water would small rainbows (spotted blue eye etc) be OK with my current fish? I'm sure the Cherries will be fine but I know the Columbians are quite frenetic when it comes to feeding. Would this be a little too much for the little Rainbows? If so, what would you recommend?

This is my first time keeping Columbians and it's only these fish that make me worry about tank mates. They're bonkers

 

[FishFinatic77]

You say you have hard water? Can you give your exact parameters? Tetras and barbs are both softwater fish.

 

[Colin_T]

Picture of the tank?

 

[Spalders]

You say you have hard water? Can you give your exact parameters? Tetras and barbs are both softwater fish.

I had one Columbian tetra come with the tank so I got him some friends
Cherry Barbs are fine with hard water, Congo Tetra are fine in hard water too but I bought the Cherries instead.
My water is 395 PPM

 

[Spalders]

Picture of the tank?

It's almost where I want it to be.

 

[FishFinatic77]

I had one Columbian tetra come with the tank so I got him some friends
Cherry Barbs are fine with hard water, Congo Tetra are fine in hard water too but I bought the Cherries instead.
My water is 395 PPM

I don't know how much of a difference 40 ppm makes, but seriously fish says that the maximum hardness for cherry barbs is 357ppm. "Hardness: 36 – 357 ppm. Wild fish will probably do best towards the lower end of this range."
You should not put fish into water that is just barely within or outside of their range. It will always lead to problems.

The maximum hardness level for Columbian tetras is 250ppm. Your water is much too hard for them. Keeping them in your water will ultimately shorten their lifespans dramatically.

 

[Colin_T]

You need to reduce the GH to less than 200ppm for them, and put a picture on the back of the tank to help them feel more secure. Some floating plants should help too. Then give the fish a chance to settle in, they probably came from softer water and are stressed in the hard water.

 

[AdoraBelle Dearheart]

The others have already covered the water hardness issue.

I also think they might be staying low because that's where the cover is. Look at your tank from the perspective of a fish that has to be alert to predators. They don't know that the tank is predator free, they're instinctively wary of open water with no hiding spaces, shadows moving across the back wall, having open water above their heads, where they would be visible to wild birds and other predators. The top part of your tank is a scary, exposed place for a fish to be!

A background on the tank, some floating plants, and some tall plants that reach the full height of the tank would give them a much more secure base to range around, and make them feel less exposed. Leave some swimming space of course, but some vallis or something on one side, combined with some floating plants with long roots like frogbit or water lettuce would make a big difference I think. Have a look at the tank in @mbsqw1d 's signature, cover like that really helps fish to feel safe, and having lots of places to hide actually means you see the fish more, since they feel secure that they can dart to safety when they need to.

 

[Spalders]

I now have a black background on the tank and more plants. I'm also going to get a few more plants this week and I've also dimmed the lighting a little. I noticed if the lights were on a soft colour like orange or yellow, the fish jump up and swim around. Any white light (literally 10-15%) will see them swim to the lower area. At the moment I have my lights (Fluval aquasky) set on 100% red and green, 75% blue and 5% white as the daylight setting and they seem OK. It's much dimmer than before and the black background will hopefully help.