Why do my fish keep dying?
This is going to be a long post, but I'm losing my mind here.
I have a 40 gallon breeder, has been running since mid June. I am not new to this hobby by any stretch of the imagination, but I am confounded and heartbroken by the number of fish deaths that we have seen in the last 1.5ish months. I believe we are now at 16 deaths!
(Yes, there is uneaten food on the substrate - I just fed them all before taking these photos. Please forgive the glare/reflections. I know it sucks lol. It's difficult to get decent photos during the day due to the windows in this room. Also there are indeed 3 thermometers in there; you're not tripping.)
There are a few things I'm worried about as potential causes, which I'll explain more below... Here are my (potentially) stupid questions:
Can expired fish food pellets kill fish within a month's time?
Can residual Ich-X kill fish if its not all been removed by water changes in time?
Are any of my fish potentially aggressive enough when I'm not looking to kill/stress out the others to the point of nonrecovery? I know next to nothing about the Emperor Tetras, except that they're larger and the males seem to "strut" and flare a little bit. Not much chasing, though....
Could there be enough oxygen depletion occurring in the tank to kill fish when my make-shift lid (made from cut acrylic "green house" plastic) drops partially onto the water surface? It is comprised of 2 pieces that were attached with plastic hinges in the middle, but the hinges will not stay put. So its just two sections of acrylic that mostly stay sitting on the inner rim of the tank. Sometimes the back portion will droop in the middle & float on the water surface. The most I've seen it come down was probably making contact with 40% of the water surface before I fixed it.
Here's the story:
We had a small amount of nitrites in the early stages for like a couple of days, but we got through that without any deaths. Small water changes, dosing of Seachem Prime, added more filtration. Never any ammonia. Today, I am registering around 5-10ppm of nitrates. No nitrites. Our tap water pH in my city is low, as is the general hardness, and the carbonate hardness. pH registers around 6 on test strips, GH and KH barely show any reading whatsoever.... I've added 2 slow-release calcium supplements over the 1.5 months it's been running (Dr. Turtle calcium blocks, they contain only calcium sulfate & magnesium chloride.. have used these for 10 years+ for various setups, primarily for neocaridina shrimp tanks and for nerite snails.. never had any issue with them). After adding these, the pH and mineral readings don't really even move at all, but I've been trying to tread carefully with these alterations.
About a month ago, we had an outbreak of ich. This was most certainly due to an overenthusiastic purchase of some beautiful neon tetras at Petco, which were not quarantined (I know I know, "bad girl!"). All of the neons died, but no other fish were lost during this time. I treated the tank for ich (ich-X & temp raised to 79F), and there have been no signs of it since. Affected fish have all improved (aside from the neons).
*I may have forgotten to do the last water change in the treatment regimen at the appropriate time (life got in the way). A 20% and a 30% water change have been done in the last 3 weeks (plus activated carbon add-ins then change-outs in the filters, and an entire filter-bag with activated carbon was added to the water column to hopefully collect any residual meds, dumped and replaced).*
What we have lost in total (not including the sickly neon tetras from Petco): 1 khuli loach, 1 diamond-head neon tetra, 1 red honey gourami, ~6 cardinal tetras, ~4 rummynose tetras, 1 Venezuelan corydora, 1 sparkling gourami, 1 ruby tetra. They have each passed away at random intervals, with no pattern that is discernable to me. Usually it is 2 or 3 fish that die each time, and it must be happening overnight.
None of these fish are otherwise showing any signs of distress or disease while they're alive ASIDE FROM: the red honey gourami I thought might have gotten stuck under the weird shaped driftwood. Found him slightly lodged under the wood, face was pale, mouth white but not fuzzy, some scales were damaged and flaking off. I put him into a hospital tank but he died the next day/overnight...
Then, a few days later the diamond-head tetra, who had some red discoloration on his back that appeared similar to columnaris. I separated him, gave first dose of Kanaplex, salt, and lowered hospital tank to ~75F. He died by the next morning. I don't know if that was the culprit, and since it is an intense antibiotic that may really harm or even kill some of my sensitive species... I have not dosed the whole tank. AND as mentioned, all of the other fish are fully-colored even when I net out the dead bodies! It is so very strange! The dead rummynose are still bright and vibrant :'(
The cardinal tetras & rummynose have been replaced since they've passed with new ones from the same fish store. The current list below is approximately the quantity that we've aimed for maintaining thus far. We've not replaced the khuli, the red honey gourami, the corydora, nor the sparkling gourami that have died. The focus has been on maintaining adequate "semi-schools" of the tetras.
Current inhabitants: (Please hold your boo's and rotten tomatoes for now) 3 albino shortfin corydoras, 3 albino long-tail corydoras, 4 Venezuelan cories, 1 bristlenose pleco, 2 khuli loaches, 3 sparkling gouramis, 2 honey gouramis, 5(?) cardinal tetras, 6(?) rummynose tetras, 3(?) glowlight tetras, 2 albino glowlight tetras, 1 black neon tetra, 5(?) emperor tetras, 8(?) ruby tetras, 1 Vampire shrimp, and some ramshorn snails.
*Most if not all of these fish are still juveniles, I've not had them very long at all and were young when shipped to me and/or bought at the store.
(TLDR I have: 10 corydoras, 1 fancy pleco, 2 khuli loaches, 3 sparkling gouramis, 2 honey gouramis, 17 cardinal-sized tetras, 5 larger diamond-shaped tetras, 8 nano-tetras, 1 vampire shrimp, handful of ramshorn snails.)
I haven't seen any concerning chasing, aggression, bullying, or hiding from any of the fish. They are all colored-up as one would hope for, they all come to the front of the tank for feeding. The rummynose, cardinals, and diamond-shape tetras often swim back and forth in a loose, school-like formation. The others' behaviors are typical for their species.
Food: I feed a few different things, and switch it up occasionally... On rotation I have: Bug Bites Color-Enhancing Flakes, Hikari Sinking Algae Wafers, Hikari Sinking Omnivore Wafers, Repashy Community Plus, and I've given them live blackworms a few times (only about a dozen in total, through a pipette, feeding like 1 fish at a time). *I was also feeding Hikari Micro Pellets, but realized today that I've had the bag for a long time...checked the date....expired 09/2024....OOPS. So that's off the table until I buy a new bag.
Filters: Two of the filters (a Nicrew internal filter rated for 20 gallons, and a large corner sponge filter that is about 7" tall and 4" diameter - idk the size rating but probably north of 30 gallons) were from an established tank that had been running smoothly for 2 or 3 years, as well as the dragon stones and the large piece of wood in the center. I have also added a smaller Nicrew internal filter (rated for up to 10 gallons), and a smaller sponge filter (probably up to 10 gallons as well).
So total filtration power is around 70 gallons.
Plants: I have mostly root-feeding plants: Amazon sword, chain swords, jungle valisneria, dwarf water lotus, crypts, aponogetons, java ferns, and some duckweed. Additionally, I am fairly sure 3 of my plants in the back are some species of draconia or perhaps bamboo (not a fully aquatic plant, I know, but they're growing and not showing any signs of dying off or rotting so *shrugs*. I'll remove them if/when that starts happening)...
I had to remove several stems of red ludwigia because of black beard algae. The stuff was covering them and would not relent. The plants started losing leaves and looking ugly, so I just removed them all.
Things I've tried to try to stop the fatalities:
Rearranged the driftwood/dragon stone in the center that I thought the gourami got stuck under.
Lowered tank temp from ~79F to ~76-77F.
3 thermometers in the tank to ensure temp is accurate (one of them is NOT).
Sank a filter bag of loose activated carbon and replaced twice over the span of a week.
Angled the internal filters outputs to push water more to the surface (create more surface agitation/more oxygenation).
30% water changes.
Serviced the filters (squeezed out in bucket of tank water, dislodged built up mulm).
Small doses of Seachem Prime (few drops) after recovering any dead fish from tank.