problematic tank!!!!

Question
We have gradually re stocked our 24 gallon tank over the last 4 months. Fish added every 2 to 3 weeks. Currently 2 catfish, 4 neons, 6 zebra danios and 4 golden tetras. 1 random black cardinal or penguin tetra, who appeared in with catfish purchase 2 months ago.

We part change the water on a weely basis and have just recently had unexplained deaths with our neons, one golden tetra and my plec. I did think by restocking we may have gone through a mini cycle a few weeks ago, so I added a small variety of plants 3 weeks ago to help and did part water changes and tried the zebras to harden off the water. The plants not doing too well.

Temp 26, PH 7.5, Currently NO AMMONIA, NITRATES a little high yesterday so a 25 % change done and okay today. Fish fed on flake, tubifex as a treat.

Had to euthanise a golden tetra yesterday as it had  some small red sores, wasn't eating so could we have some sort of bacterial problem.

The random fish seems a little aggressive to all others in the tank. He is worrying the female danio to the point of hiding today so I think her over zealous darting about is down to him. Another male danio is hiding and not moving about too much, as was the golden tetra yesterday, although no visible sores on the danio.

Could it be the random fish stressing the others to death or is it more likely something else going on like a bacterial infection. We have had some small problems with nitrates but now under control.

We have lost 6 neon tetras, 5 black neons, a plec and a golden tetra over the last month or so. Apart from the golden no visible signs on any of the fish.

I have decided not to restock until this is sorted out.

Thanks for any ideas and help.

Jackie

Answer
Hello Jackie,
No matter what, whenever you start out a new tank there will be some losses. So it's not entirely unusual to lose one or two fish. However, in this situation you happen to have a few fish who are not part of the pack, and this can make them nervous and/or aggressive, which make other fish nervous...and so goes a vicious cycle making your fish nervous and therefore their immunity weakens and they become sick. Any fish that has been exposed to prolonged stress will become sick.
Try to have 4 or 5 of the same species at all times, when it comes to these small tropical community fish. Danios especially have been known to become aggressive fin nippers when they are nervous. Having more of their fish buddies instantly calms these fish down - it's a survival instinct. Suddenly they have more eyes watching out for them and they don't constantly have to be on guard.
So, try adding just enough fish to have a small school of each species already in your tank, add some aquarium salt for stress relief, and move around the decor a bit so no one will become territorial.