Multiple cherry barbs died

  • #1
Water volume remaining consistent (20g long tank)
Tank Running since January
Two filters (Seachem Tidal 35)
Heater is working
Water temp is 78
More on the stocking below

Every other week water change (25%)
Just use tap water treatment
Substrate is vacuumed as much as possible

*Parameters - Very Important
Tank was completely cycled before adding original inhabitants
Use API Freshwater Master Test Kit to test the parameters
Current parameters...
Ammonia: 0 - 0.25ppm
Nitrite: 0 - 0.25ppm
Nitrate: ~5-10ppm
pH: 7.8 (has remained consistent)

Feed fish small amount of TetraMin tropical flakes daily. Occasionally feed freeze dried blood worms.

Illness & Symptoms
Cherry Barbs have been in the tank since ~February. In fact one was born in the tank and has grown up in there.
Details below. No treatment started. No symptoms except death.

Explain your emergency situation in detail.
I've had 6 Cherry Barbs, two nerite snails, and 4 shrimp (2 cherry, 2 ghost.. who disappeared after adding the Barbs.. but two of them to reappeared recently) for months. No problems.

Last Friday I added 6 new Oto catfish to the tank. They were acclimated for a couple hours before being added. Within 24 hours (Sat) one oto died. I did about a 20 percent water change. Two days later (Mon) I noticed an oto and a cherry barb died. Tested the water.. seems ok. A couple days of peace. This morning (wed) two cherry barbs turn up dead.

The barbs were completely fine until I added the otos.. I don't see anything disease- or behavior-wise (although I am new to the hobby, don't know what I'm looking for). Otos came from a reputable LFS and the ones that are left seem OK (very skittish and move very quickly when they see me). The only problem with the tank right now is I have some blue green algae.. but it's not completely out of control and I planned on treating it starting this weekend.

In the attached picture it looks like maybe there is an issue with the gills? They were not acting strange yesterday and, again, I'm not sure what I'm looking for.

Thanks for your help!


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  • #2
Hi, kind of hard to say what happened. If a fish died and was left in tank for a few days it will build up the ammonia and nitrite in the tank. Fish can't deal with ammonia or nitrite well and your readings should have 0 for both. What happened was probably your parameters spiked from adding new fish which your filters wouldn't of been used that sort of bio load. Fish died causing worse parameter swings and possible ammonia burn on the gills from the pictures. I would try to change water every week in smaller aquariums. If you are only going to change water every two weeks I would do at least 50percent. 25 probably won't be enough. How often do you clean the filter?

  • Thread Starter
  • #3
Thanks Ksway ... I also read that potentially moving decor could cause gas trapped under the substrate (it's a dirted tank) to poison the water. I definitely moved some rocks.

I clean the filter somewhat sparingly. Never in tap water (always in the water that I took out of the tank). I did just clean one of the filters the other day (which is where I found one of my cherry shrimp living!).

Should I place the rocks in the bag ever? They seem relatively clean after I agitate them in the removed tank water. I wasn't thinking they needed to be replaced.
  • #4
Yes it can kick up gas but for how old the aquarium is I wouldn't imagine that to be the case. When you disturb the substrate it can definitely cause ammonia spike in the water and in your case it's dirted with natural soil so could of definitely caused an issue. Did you cap the dirt off with a thick layer of sand? What type of filter do you have? Is it filled with just sponges or us there biomedia in it? Generally a good practice is to clean the sponges in your filter in tank water every month as these will store all the poop and waste in them, so if you leave them for a long time this all builds up and cause parameter swings.
  • #5
If you had gas in the substrate it would smell like rotten eggs. You would have noticed it as you moved stuff around. I agree that adding new fish raised the bioload and combined with you rinsing your filter caused your ammonia likely spiked then you had a chain reaction. Otos can be sensitive and are actually hard to keep alive for various reasons. Any small tank needs good water changes frequently as any changes can have a large affect since there isnt much water to dissipate into. Also the filters should be rinsed pretty regularly because of the amount of junk that can build up.
  • Thread Starter
  • #6
Ksway ... I do have sand over the dirt. I think over time it has mixed a little though... I may get to the point where I just start up a new tank sand only.. or using some other substrate. Not loving the dirt! But I have not noticed any parameter swings at all... so I think I am probably doing enough to clean them. I hope! I will try to pay closer attention to the frequency.

awilkinson871 I have a very poor sense of smell.. but I have noticed the tank has an odor. I attributed that to the dead fish sitting in there overnight.. either that or the blue green algae.


  • #7
I'd say the dirt is leaching into the water if it has kicked up from the sand. You would want at least an inch of sand over top 2 inches would be ideal. If you go longer than a month with out cleaning the sponges it will definitely contribute to poor water quality. Most filters that comes with tanks don't offer enough filtration in the first place so it is very easy to clog them up.
  • #8
I have to wonder if the otos brought in a disease or parasite.
  • #9
Possibly, Id say it's not the root of the problem though. Most aquariums most likely have some diseases in them but healthy fish don't normally succumb to them as they are able to fight it off with a healthy immune system when parameters swings happen it causes the fish stress and weakens there immune system and then they are susceptible to disease. You had ammonia and nitrile in the tank so this would be an issue for otos like the previous poster said they aren't a hardy fish and can die off at the beginning very easily. They don't ship well and often come into stores not in great health.once you can keep them alive for a while they become strong and more hardy.
  • Thread Starter
  • #10
No more deaths. I did a water change the other day after realizing it might be some gas of some kind poisoning the water (that I couldn't account for in the parameters). Who knows if that was the case.. but the remaining 4 otos and 3 cherries are alive.
  • #11
That's good to hear! It's about a 1% chance that it was a gas build up, in a tank that is 7 months old. More likely fish just were not healthy fish or water quality as your tests showed nitrite and ammonia in water. The soil is probably most likely the issue. If not capped with sand properly it can release ammonia in the water which fish can't deal with.

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