Invisible Stalker - Losing Fish w/o visible signs

[YellaFox]

Basics
17G freshwater planted tank running about 18 days, midsize canister filter, w/ Ziss air stone, in-tank heater. Water clarity is good, no "pond" smell, tank interior seeing respectable algal growth (green dust, spot, brown diatom). Reducing lighting duration to combat, no fertilizer or CO2 in use.

Temp: 74F
PH: 7
Ammonia: 0
Nitrate: 0
Nitrite: 0
GH: 30
KH: 40

Hardscaped, planted, and ran tank w/o fish for the first week, testing each day. Confirmed stable, added 5 Red Phantom & 5 Cardinal tetra around day 10. Zero issues, fish displayed healthy color and relaxed schooling behaviors.

Next day, added 5 panda corydoras. Roughly 8 hours later one began showing swim bladder / coordination issues. Found dead later that evening, maybe with slight film on one eye? Inconclusive.
- Next day, another panda down, filmy eyes.
- Next day, another panda down, no visible issues.

This past Friday evening I noticed both remaining corys had visible white cottony "dust" indicative of a bacterial infection. Saturday AM I picked up Maracyn on the advice of the Co-Op crew, begin dosing for the correct water volume. I am now consistently losing one fish per day, with the following sequence:
- Visible loss of coordination / fine motor controls, with symptoms worsening over several hours
- Capture affected individual in fine net, suspend in gentle return flow to ensure available oxygen
- Death

It is now affecting all tank species (except the Amano shrimp), BUT my two corys remain hardy! Signs of infection are diminishing. I am hesitant to change the water, as that will affect the Maracyn protocol, and am completely baffled. Since the weekend each lost fish has zero visible stress indicators / no signs of illness / good color, until rapid decline sequence outlined above. I have also considered adding UV to the return loop, but the Maracyn instructions advise against it.

I've attached pictures of our most recent loss (the white things that look like teeth are bubbles). This feels like an issue with bacteria suspended in the water column, but the onset of illness seems quite fast.

Ideas?

[YellaFox]

On 8/17/2021 at 4:37 PM, Tankseeker said:

Well first off I think your tank is overstocked and did you get the fish from the same shop?

Yup, same place (Aquarium Co-Op). All fish looked healthy & fit when they joined the tank, don't think the source is at fault.

My canister is running just shy of 150g/hr, media volume is 2+ liters, practically as much BioMax as I could fit. Current population is 26 fish. Interior tank flow is gentle ... but maybe we've got too many water changes per hour?

 With overstocking, I would usually expect to see degraded water params, which I'm just not getting 🤔

[Littlefish]

GH and KH are ppm?  Very soft, right?  I only have used dkh testers. Would the ph be swinging at night and causing stress induced illness?

[Colu]

I think your tanks not cycled yet as your not seeing any nitrates as you add the  fish over a two day period you could have missed an ammonia spike cloudy eye that your describe is usually caused by poor water quality what I would do is small daily water changes add prime daily and treat with kanaplex in food stress could have caused the out break of a bacterial disease here's a food recipe for kanaplex

Edited August 18, 2021 by Colu

[Patrick_G]

I agree with @Colu , your tank is probably not cycled yet. You should see nitrate rise as ammonia and nitrite drop to zero. A fishless cycle often takes more a few weeks. Now that you have fish I’d check parameters every day and use Seachem Prime according to the instructions for neutralizing ammonia and nitrite. 

[YellaFox]

On 8/17/2021 at 6:15 PM, Patrick_G said:

I agree with @Colu , your tank is probably not cycled yet. You should see nitrate rise as ammonia and nitrite drop to zero. A fishless cycle often takes more a few weeks. Now that you have fish I’d check parameters every day and use Seachem Prime according to the instructions for neutralizing ammonia and nitrite. 

With this tank I tried something new, using Activ-Flora substrate, which (supposedly) provides a very rapid start. Dosing with a bit of fish food, I did see low ammonia, then trace NO2, NO3, but you may be right with the fluctuations. I've been trying to test every day, maybe will add a 2nd test to see if it's swinging. Will also look into KanaPlex.

@Littlefish Yes, GH & KH are ppm. Municipal water source is super soft, I added several ounces of crushed coral to the canister to boost minerals.

@Tankseeker Definitely -- though am a bit hesitant to add too many things at once 😅

[Gator]

You're introducing blackwater fish to a hard water tank as evidenced by your KH and GH, and your water temp is too cold for these fish. 

Raise your water temp to 85 degrees and keep it there, this temp will fight diseases without the expensive meds.

Add about 1/2 teaspoon of Fluval peat pellets in a mesh bag to your filter and watch the change. Your water will still be clear, but will take on a yellowish tint, your fish will be more active because the higher temp is what they prefer, and the softer water is more like the water they originally came from.

[Patrick_G]

A zero Nitrate can also mean you’re getting a false negative on the API liquid test. It’s important to follow the instructions exactly to get the correct results. It’s ok, many of us have done it! 😀

What are your current parameters? 

[Patrick_G]

On 8/17/2021 at 9:27 PM, Gator said:

You're introducing blackwater fish to a hard water tank as evidenced by your KH and GH, and your water temp is too cold for these fish. 

Raise your water temp to 85 degrees and keep it there, this temp will fight diseases without the expensive meds.

Add about 1/2 teaspoon of Fluval peat pellets in a mesh bag to your filter and watch the change. Your water will still be clear, but will take on a yellowish tint, your fish will be more active because the higher temp is what they prefer, and the softer water is more like the water they originally came from.

I think 30 ppm is very soft water so it should be ok for these fish. I agree that 74F might be a little low for the Tetras but is just about right for Panda Corydoras. 

[TankofFish]

On 8/18/2021 at 12:27 AM, Gator said:

You're introducing blackwater fish to a hard water tank as evidenced by your KH and GH, and your water temp is too cold for these fish. 

Raise your water temp to 85 degrees and keep it there, this temp will fight diseases without the expensive meds.

Add about 1/2 teaspoon of Fluval peat pellets in a mesh bag to your filter and watch the change. Your water will still be clear, but will take on a yellowish tint, your fish will be more active because the higher temp is what they prefer, and the softer water is more like the water they originally came from.

 panda corydoras, not sure they will be able to handle that heat.

Hate to say it this way but this tank was over stocked and was a ticking time bomb and on top of it the tank may not have been cycled to handle that big of bio load (young tank)