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Discussion Starter · #1 · (Edited)

I have a 36gal tank that was set up last summer and was well cycled, with all fish living very happily. I had to give fish away because they were breeding so much (sign of happiness?). I went away for two weeks in December, and have been fighting an increasingly difficult battle to keep my fish alive since. I'm new to fish keeping (this is my first foray) so would appreciate any help or guidance!

What it used to be:
Water Plant Plant community Green Pet supply

  • 7 neon tetras
  • 8 orange laser corys
  • used to have about 20 guppies of various sizes

Tank substrate + plants:
  • substrate is petco white sand
  • 2 pieces of 10inch long driftwood, tannins have all come out now
  • approx. 10 Java ferns (about 5" in height each)
  • 3x 1lb grey stones (sorry, not a geologist) I found while hiking - I boiled these in water before introducing into the tank back last autumn, no issues from these.

  • Heater: 1x adjustable
  • Air pump: 3.5W TopFin airpump going to a hygger circular air pad + an air stone shaped in a bar (it is 8" long but only 3" of it bubbles, prob poor quality stone)
  • Filter: 1x submersed fluval U2, set with venturi above water level to aerate the water

Water conditions:
API test strip readings:
  • nitrite and nitrate at 0ppm (before the death spiral started, this was at 0ppm nitrite, 20ppm nitrate)
  • pH at 6.5
  • KH at 0
  • GH at 0
API ammonia liquid test kit reading
- ammonia at 0ppm - 0.25ppm
Temperature: 75degF, checked using two separate digital thermometers

  • crushed fish flakes, only as much as fish can eat in 1 minute, once daily every other day
  • in addition, 1 frozen gum drop of bloodworms per week

Usual cleaning cycle:
  • 20% water change, once per week
  • I would take the sponge and charcoal pad out of one side of the U2 filter and squeeze it in a bucket of fish tank water, once per week, alternating sides
  • I would add Tetra AquaSafe plus to the tap water before adding to the tank

* reduced feeding to once every 3 days, no bloodworms. But also no water changes (had the cat sitter feed the fish)

Ok, now to the fun (or not so fun part) of problems and attempts to fix:
1. after holidays, did a 50% water change and cleaned one side of the filter as normal
2. 1 week of normal fish life followed, ammonia at 0ppm, nitrite at 0ppm, nitrate at 20ppm
3. I wanted to change the filter (U2 is rated up to 30 gal tank, mine is 36gal), so I bought a Fluval U4 submersible, took half of the bio-hoops from the existing U2 and swapped it between the fresh ones from the U4. Also took the sponge from one side of the U2 and added it to the U4. Ran both filters in parallel
4. from here the ammonia started climbing to 0.5ppm. Reduced fish feeding to once every 3 days
5. did daily 25% water changes, but fish started dying. Didn't want to do too many water changes, ammonia could only get down to 0.25ppm from changes
6. added Tetra SafeStart concentrated plus to try add bacteria in. Also used ammolock to try and get down to 0ppm
7. water then started to turn slightly cloudy white, with guppies hanging out at the top of the water, sometimes near the filter, sometimes on opposite corner of the tank
8. took this as a sign of the tank starting to cycle, but guppies not having enough air, so turned on the aeration on both the U2 and U4 filters (I didn't do this before, the 2x airstones seemed to work fine)
9. guppies continued to die off, so to eliminate issues I took out the U4 filter, putting the media back into the single U2 that I left running
10. I used to have a mesh lid so I can keep the hood open without fish jumping out to help cool the water during the summer, and found this was severely rusted - I figured condensation could be causing the rust to drip into the tank (whenever I did a water change, about 30 drops of water that was sat on the rusted parts would drop down when I moved the hood), so I removed this mesh grid completely

I did a 20% change last night and the guppies seem better whenever I do a water change. But I end up picking up several dead guppies every morning now. Tetras and Corys seem to be fine, swimming at the middle and bottom of the tank.

Ordered a bigger air pump and additional air stones which should arrive today, as the guppies are still huddling at the top of the water and near the air pump. I don't know if I'm doing too much and should just ride it out, but at the same time I don't want more guppies to die (I'm down to the last 4 or 5 now).

Updates (added images)

Water Plant Plant community Green Pet supply

Note; the net nursery was added to separate a male that was hounding the females too much. Soon after this I gave away a few males, and added two females - see my next post related to this...

Water Plant Plant community Vertebrate Nature

Guppies all staying at the top of the tank
Running both U2 and U4 filter with aeration in response. U4 was turned right down to have the same flow as the U2.

Plant Water Vertebrate Nature Leaf

Guppies have all died/been removed into a separate tank.

Window Shade Wood Interior design Automotive exterior

Separate 10 gal tank, with U4 filter, fresh water (not from fish tank), airstone and heater
Only 2 guppies are here, but seem to be doing well now

Any help is appreciated.

2 Posts
Discussion Starter · #3 ·
Thanks @FishHoarder14 for the reply!

Pretty much all my guppies have died bar 2. Yesterday was brutal, with about 8 bodies. By that time I took the last 3 out and put them into a separate bucket, which with a rush trip to Petco was replaced with a separate tank with its own heater and air pump.

One guppy died overnight, with just two remaining now. They seem to be doing well in the new tank but will need to monitor closely.

Window Shade Wood Interior design Automotive exterior

Tetras and corys still doing fine in the main tank. Tested 0ppm ammonia in both tanks, so did a very light feeding. All fish seemed to respond well (not doubt they are hungry from not being fed a few days).

New theory on why this happened: around the same time as things went south I introduced two new female guppies + 4 small laser cory's to the tank from my LFS. Didn't quarantine them before adding to main tank. A few days later, one of the female guppies developed a light rash on her body; I didn't think it was much of an issue, but then she was one of the first ones to die, along with the other new guppy I bought. Wasn't the first to die, but in the first quarter of fish that went. Could it be a guppy specific disease, hence why it didn't affect the corys or tetras? Counter arguments are that ammonia levels did go up at the same time, though that may come from the fish dying overnight and me only netting them out in the morning/when I see them (sometimes they are hidden in the wood/ferns).

The rash looked like this (not my photo): see the light area near the tail. Though on my fish there were two blotches, so double the amount here. Tail itself was fine, unlike in the photo.
Water Organism Underwater Fin Fish

Source: FAQs on Guppy Diseases 3

Will update again as things go on, but lessons learnt so far:
  • evacuate fish that are poorly early
  • quarantine new fish first to be safe
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