May I ask where did you get the fish from? Was it a smaller Mom and Pop shop or a Big Box pet store like Petco or Petsmart?1. Size of tank? 29 gallon
2. Water parameters
a. Ammonia? 0
b. Nitrite? 0
c. Nitrate? 20-30
d. pH, KH and GH? Ph 8, not sure of others
e. Test kit? Api drops
3. Temperature? 77
4. FW (fresh water) or BW (brackish)? FW
5. How long the aquarium has been set up?2.5 months with no fish but dosing ammonia, 1 week with fish
6. What fish do you have? How many are in your tank? How big are they? How long have you had them? 7 Black Neon tetra, 7 espi rasbora, 6 zebra danio, 6 sterbi corydora
7. Were the fish placed under quarantine period (minus the first batch from the point wherein the tank is ready to accommodate the inhabitants)? They were all added at the same time from the same store.
8. a. Any live plants? Fake plants? Live plants, amazon sword, dwarf hairgrass, anubis hornwort
b. Sand, gravel, barebottom? Sand and gravel
c. Rocks, woods, fancy decors? Any hollow decors? 1 piece of driftwood
9. a. Filtration? Aquaclear 70 and a sponge filter
b. Heater? Yes
10. a. Lighting schedule? What lights are used? 4 hours on, 3 off, 4 on, 13 off
b. Any sunlight exposure? How long? None
11. a. Water change schedule? Only one completed since adding fish
b. Volume of water changed? 25 or 30%
c. Well water, tap water, RO water? Tap
d. Water conditioner used? Yes
e. Frequency of gravel/sand (if any) vacuumed?
How often are they fed? Daily
13. a. Any abnormal signs/symptoms? Red anus, some had red bodies, breathing heavily, all a few hours before dying. Everyone else acting and looks nornal. Losing one or 2 fish each morning
b. Appearance of poop? Normal
c. Appearance of gills? Normal
I have had a planted tank setup with no fish since feburary. I had it cycled by dosing ammonia. I added 7 neon tetras, 7 espi rasboras, 6 zebra danios, and 6 sterbi corydoras about a week ago. Everyone seemed to acclimate fine. The next few days I would find a dead tetra or 2 each day. I kind of chalked it up to the tetras not being the healthiest fish. I didnt notice any odd behavior until the last one to die(still have 2 left) the night before I found it, it looked to have a shiny or maybe white spot on its dorsal fin, a red anus, and was kind of slow swimming. Every other fish this whole time has been perfectly fine and normal.
Next I had a cory dead this morning, about 6 days after adding the fish. It had a very red anus and its chest and behind the gills was red. I also noticed two more corys acting odd. Darting to the surface and sitting very high up on plants and breathing heavily. The other corys and the other fish again acting perfectly fine and not breathing heavily. I did a 25% water change and the two corys tripped out darting around, rolling over, and died. Both had very red anus.
Water parameters are good and stable all week. 0 ammonia 0 nitrites and 20 or 30 nitrates. PH is a little high I think at around 8 but has been stable and is the same as my tap. Dosed with dechorinator too.
Am I wrong to think it may be infection or parasite rather than water quality? I would think water quality would affect more fish at the same time but everyone seems to be fine. Its like their anus turns red and they die a few hours later.
This picture is the cory that died over night, the other corys that died didnt have as red of a body but still had red anus. View attachment 845071