New Tanganyikan Setup - Initial Casulaties

I have a 26 gallon bowfront aquarium (roughly 2' long, 20" h, 10" d). All my water chemistry is fine - trace elements are sufficient, temp is fine and nitrogen cycle is perfect.

Over the last week, I've stocked the tank with the following Tanganyikans (length head to end of tail):
3 cyp leptosomas (1.25")
2 n. leulupis - pair (1-2")
1 n. tretocephalus (2")
2 j. regani (1.25")
2 l. oscellatus (1")
2 n. brichardi (1.25")

The following fish have died: 1 cyp (was replaced), 2 brichardi, 1 regani. All within the first week.

There are no visible signs of any illness on the fish - no signs of Bloat or Ich. I have found the fish 1 or 2 at a time in the morning when I check the tank - seems like the deaths occurred during the night when the tank was dark.

The male leulupi and tretocephalus are fairly aggressive fish, so it could be stress related. however, there is plenty of room in the tank and the oscellatus have been harassed way more than the other fish. in fact, the brichardis were harassing the cyps.

any ideas what happened? is this anything more than initial tank setup/stocking pains as all my fish adjust to their new world? do you think i definitely overstocked? i wanted to provide enough company to chill out the male leulupi via overcrowding (since they are all relatively small and young) as he started terrorizing the neighborhood and aggressively defending his territory as soon as he was placed in the aquarium.

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This is a response I received:
Robin
Moderator

Hi,

A few things stick out to me from your post as possible problems.

First of all, the size of the tank. It's way too small for most species of cichlids. Your plan to over-stock in an effort to deal with the aggression of the male leulupi is along the right line of thinking but unfortunately the tank is just way too small for even this to work.
My advice: return all but the shellies and build the tank around them. It should make a really nice tank for them. Go to the profiles section and also the 'cookie cutter' section for more on keeping this species.

What are the actual numbers of your water parameters: ammonia, nitrite and nitrate? What method did you use to cycle the tank? Did you add all the fish at once? What kind of test kits are you using.

Water quality may or may not be an issue with this tank but I think the most likely cause of death in the fish is aggression from other fish.

Please post back with any additional questions or concerns.

Robin

You might also post a question in the General African folder or Tany Folder--post your tank size and list of species you are keeping and see if anyone in either of those folders can suggest what stocking changes you need to make.

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This was my response - I've had another regani die:

Robin,

Thx for the post.

I've since had some more casualties - pretty sad, but I think you were spot on that I was overambitious given my tank size (and the fact that it's just not long enough and doesn't provide enough bottom territory).

Ammonia and Nitrite is 0, Nitrate is around 0-12 mg/l depending on if i just did a water change. Did a fishless cycle and added all the fish at once. There was no spike in Ammonia or Nitrite once I added fish.

With the dead of the reganis and brichardis, I'm left with:
1 Tretocephallus
2 Leulupis
2 Ocellatus
3 Cyp Leptosoma

I might switch out the Tretocephallus for a Black Calvus, but the Treto is a beautiful fish (though much bigger than the rest and aggressive). The Cyps pose no issue at all and swim in the open water.

I'll also post in the Tanganyikan section.

Thanks.