Backyard Aquaponics
A place to discuss aquaponics

Hi everybody, I am new to the aquaponics and built my first IBC aquaponic. Everthing works fine so far. All of the sudden, the water turns light (very light) green and the fish are dying. Here are my water test results:

N03= 0
N02= 0.05
GH= 7
KH= 13
pH= 7.6
CL2= 0
C02= 10
NH04= <0,05

Anybody any idea what could be wrong? Thanks for some help

Tom

Hi Tom. Sorry to hear about the fish deaths. It's pretty difficult to diagnose things like this but there really isn't enough information here yet to give it a shot. The light green water is probably just some algae but doesn't sound like enough to cause problems at this time. Having said that, algae can cause the pH to fluctuate and can lower the oxygen levels in the water if there is too much of it (might be worth checking out). Any idea on the following - Ammonia levels, water temperature. Do the fish appear to be gasping for air at the top or hanging out at the water inlet or are they down along the bottom of the tank? Do you see any flashing or any other external signs or symptoms of possible infection?

What type of fish are you growing?

Hey Scotty, since I am in Germany and aquaponics is at its very first beginning here, I decided to grow tench or doctor fish (Schlei). Interesting is, that at the beginning the fish were down at the bottom of the tank even hiding and as soon as they got sick, they came up gasping for air but not much...

I'm not familiar with tench but based on the reading I could find they are tolerant to low oxygen levels. How many fish are you trying to grow and how big is your system?

Based on what happens to many people your system may have had an ammonia or nitrite spike. If this doesn't kill them outright, you'll often lose a few fish at a time over a long period (weeks) - often they all wind up dead. Much of the damage is to their gills so they have troubles and wind up gasping for air. Until we know what's happening, I would treat your current situation as though this is what happened and add additional aeration.

I would be careful on feeding them and I would look for additional dead fish on the bottom (although I doubt you have any, they don't always float).

If you haven't salted your system to help the fish with stress, building a slime coat, and preventing damage from high nitrites then I would do this as well. One part per thousand is the usual dose and the salt should not have any anti-caking agents or be iodized.

Don't forget to answer as many questions as you can from my previous post

What unit is the CO2 measured in? ppm, mg/l?

At 15 degrees C, water that is in equilibrium with air (saturated) will contain around 10 mg/l of O2 and 0.6 mg/l of CO2. This makes me wonder if your reading of 10 for CO2 might indicate the cause of death. The micro algae that's causing your water to turn green will cause the O2/CO2 levels to fluctuate with the light cycle of day and night.

Have you monitored the behavior of the fish throughout the day? Do they gasp at the surface more in the morning than the evening?

Your PH is not the problem with a KH that good (no fluctuations).
Notice you have a bit of Ammonia & Nitrite,but 0 Nitrate.I don't think the system has fully cycled.
When fish have been exposed to Ammonia or Nitrite poisoning,they start gasping for air because their gills have been damaged (sometimes).

Before this post, I'd never heard of KH and GH, and therefore never tested it.
do i need to worry about it?

I'm not an expert on this topic but I think it depends on how you run your system - regular AP, split system, or Recirculating Aquaculture system - and also what you're using to adjust your pH (some things add to carbonate hardness and others don't). My personal opinion is that regular AP systems are very forgiving but split systems and RAS you should watch the carbonate hardness (KH) and adjust if needed. The down side of not doing this is very fast pH swings that can kill the fish and affect any biofiltration as well.

I'm a backyard grower, I don't spend much time running water quality tests in my regular AP (this is pretty common with older systems) but I'm not pushing the stocking limits and I do occasionally adjust the pH using CaCO3 based products that help raise the carbonate hardness. There are other strategies using hydroxides which don't effect the KH (worth a look through the threads on BYAP or check out Nate Storey's videos pH adjustment on youtube).

Commercial growers should pay a lot more attention to nutrients and water parameters than someone who's a backyard grower since messing up is a lot more expensive so you want to get it right.

Meanwhile after all my fish died I changed the fish. Same problem, fish are dying again. Looks like a desease. Does anybody have any idea what it is? Pics enclosed.

Looks like it could be Saprolegnia aka water mould. Salting the system should help surviving fish, and disinfecting and starting over would eb a god idea before trying another batch.

Where did this fish come from? Is it a channel catfish?