Backyard Aquaponics
A place to discuss aquaponics

Hi all,

Got the system set up, 1500L tank, rainwater + salt additive from pet shop (the guy told me this amount would treat 1500 litres). After 1 day of putting in the fish, 10-20 had died. More have died gradually throughout the first week and now only 20 remain alive.

Scoria gravel and marble for the growbed medium was sourced from a standard garden landscape supplier. Washed it thoroughly to the point where you can see the bottom of the fish tank. Still may be contaminated?

System was pumping (flood and drain) for several days before fish arrived.

Suspicions:
Many fish were refusing to eat in the first couple of days, and also feeding regime was sporadic (unable to feed more than once in morning + once after dark for the first couple of days). Ausyfish guy said that perhaps they got out of the habit of eating and started starving? Change in food + chemically different water may have contributed to this as well. Also, didn't get an aquarium aerator into the tank until two days ago, perhaps oxygen deficiency?

Remaining live fish appear to be swimming around happily after 1 week.

Any input is appreciated as this is a very distressing (not to mention expensive) loss.

Oxygen looks like the culprit

I'm in my first week of 50 SP and despite preparation I dread an outcome like yours. Sorry I can't help but I feel your pain.

Derek

did you test the water, ammonia nitrite, and nitrate when they all started dying?

When you say the system was pumping for a couple of days before the fish were added, was that just the rainwater and salt? or did you start the cycling process?

Lastly how much were you feeding them?

it may have been a severe ammonia spike.....

What about ph? unless they were gulping at the surface, I doubt it was DO. (IMHO) Can you test the ph and let us know? The other thing I wonder is temps. Not so much that our cold temps will kill them, just maybe they were reared at temps in the 20's then all of a sudden they are in water in the teens. Do you have a test kit? If so, do the etss re ph, ammo and nitrites. Remeber while your system is cycling up, you will want to feed lightly anyway.

Water was flooding the growbed and draining for a few days straight prior to getting the fish. Salt was added a day or two before the fish arrived and the cycle kept flooding and draining.

Fish were dead on bottom of tank, not gulping at surface. No floaters at all actually.

pH was tested and was about 7.4-7.5
Ammonia didn't even register.
Didn't have test kits for nitrate or nitrite, but as there was no detectable ammonia we thought it wouldn't be a problem. Besides, 100 fingerlings in 1500 litres is a miniscule fish : water density.

In the first 2 days, Dad couldn't get to feed them apart from once first thing in the morning (very cold I imagine), and once after dark. When he could feed them more regularly, they were fed more than they could consume. In fact what he thought was grit on the bottom of the tank is a very large amount of uneaten fish pellets. Could this be the problem?

Would uneaten fish food be consumed by, say, aerobic bacteria or other microbeasts that deplete the O2 levels?

the uneaten food is broken down into ammonia and other waste products that are bad for the fish. That is why over feeding is very bad. You should only ever feed what they will eat in five minutes, especially when cold.


Also if this is what happened then the pH of the water is very important as higher the pH the worse the effect. Also when it is cold it can take up to three months to fuly cycle a system so that it can handle loads of ammonia. Sorry but you might of just taken one for the team to highlight the importance of slow feeding at the start and testing when you are getting started.

Sorry,

Re-tested ammonia, carefully scooping the water sample from right near the pile of uneaten pellets. Still no reading - the sample didn't even take on any colour when the indicator was added.

pH was pretty much exactly 7.4

Still, we fished out as much of the uneaten food as we could to prevent contamination.

The remaining 20-odd fish are swimming and darting around the place, looking quite happy.

When you say 3 months to cycle through, do you mean that is the time taken for the bacteria to build up in the growbed naturally?

that is the time that it may take to cycle the system and by tat I mean, the time it takes for the cycle to go through the ammonia spike followed by the nitrite spike and eventually leading to the nitrate spike, by this time the ammonia and nitrite should bw zero. This can be as shot as two weeks in summenr but in winter can take a lot longer.

So you added salt to 1,500 litres - the amount should have been 4.5 kg to build up to a saline level of 3ppt.

100 fish were added - were they fingerlings?...if so then DO shouldn't be a problem

I don't think starvation was the problem either - the fish normally don't feed immediately and should be fed sparingly for the 1st week.

My immediate thought was the system hasn't cycled and ammonia levels are the culprits.

This is easy to say in hindsight but you might want to try testing new systems with a few goldfish (10 - 20) and cycling before putting in a bulk amount of fish.

What to do:
use the remaining fish to cycle the system
feed sparingly
regularly check ammonia levels until it has peaked then dropped to zero (this could take 2 - 6 weeks, dependent of water temp)
then regularly check nitrite until that has also peaked and returned to zero ( this will take a couple of days after ammonia gone to zero)
above all feed sparingly - keep the fish hungry (and alive)

If ammonia/nitrite levels get above 1, start doing water changes

There is some specific info on max levels to water temp/PH in the useful info section courtesy of Steve

Hope this helps

I do believe that the system was not ready for that number of fish. How big were they on average when you put them in. I agree totally with Nick any fish tank must have sufficient biological filtration to handle the ammonia and nitrite that is in the water. Take a sample of your water to a fish shop, and get them to test it.

Personally I wouldn't have fed the fish for at least 3 days after getting them because of this reason. Uneaten food is a huge fish killer. Have you done any water changes since the fish started dying? If not do so soon!!! Exactly how much salt did you put in?

The water flowing back from the grow beds should have provided enough oxygen. How long is you cycle time? Does it run at night?

Have a think about possible sources for contamination. Was everything clean? Brand new? What else is in the tanks? Was there any chemicals in any of the components at any stage? How long did the purple PVC glue have to dry before water was pumped through them?

Usually the cause can never be completely narrowed down but you can always find a way to remedy the situation.

jimmy everyone has covered it pretty well.

I know you have said that the ammonia didn't register, but i had half your fingerlings in an uncycled 1000l tank and the ammonia went through the roof.

with the test that i use an ammonia reading of zero is a yellow colour.

Can you post a pic of the ammonia test you have.

i know that the fish to litres seems insignificant (and it IS for a cycled system), but an uncycled system is a different story.

I wuld LOVE for you to do an ammonia test with a different test kit. are there and AP'er near by?

regarding the aquarium salt, give it a miss, not needed. value added sales

get to know your nitrogen cycle well (in the useful info section.)

Don't get me wrong, if the ammonia IS zero then so be it, but i would have been more convinced with a low reading than a ZERO reading.

even in a fully operational mature system, if you double the amount of fish overnight from say 50 to 100 you WILL get an ammonia spike.

Steve

The salt added was a bluish coloured salt from the pet shop and would have been between 0.5 and 1kg, nowhere near 4.5kg. Is there a chance the water is TOO fresh? Unlikely is my guess.

Ammonia test kit has five circles ranging from a very pale yellow (0.025ppm) to an orange/brown (2ppm). I've just noticed that the instructions tell me to look down the vial (not looking through it sideways as I did before). Doing this tells me there is actually somewhere between 0.025ppm and 0.1ppm, so I was wrong to say zero ammonia. "User error"!

But that's still low ammonia levels compared with 1ppm, unless it's sitting as a "cloud" of ammonia-rich water right above the uneaten food. Yesterday's sample was taken a few inches above the uneaten food - (that was the extent of Dad's arm in the cold water).

Bear in mind we're talking about 100 tiny little fish, of which only 20 have actually survived the week, so the number of fish actually actively contributing to ammonia production over the week has been substantially less than 100. Meanwhile the number of dead fish contributing to potential contamination (?) has been high.

Re: Cycle time, it's 15 minutes pumping, followed by either 30 or 45 minutes draining (it varies). It runs like this 24 hours a day.

If uneaten food truly is a known killer of fish, then I'm sure that's the problem because we fished out probably a CUP full of uneaten food yesterday. We simply didn't know it could be dangerous to overfeed (first time keeping fish in this intensive way).

Is it possible that uneaten fish food could have killed the fish, even if it did NOT lead to a noticeable ammonia spike?

Weird - but for your tests, ammonia would be my guess too. As said before the issue with the uneaten food is that it will result in ammonia as it rots. The uneaten food itself (particularly in that volume of water) should not have killed the fish - just the ammonia produced. I too wonder if your testkit works.

I wonder - how readily does ammonia "homogenise" in water? Might be a long shot, but is it possible that there could have been "pockets" of ammonia forming in between pumping (when the water is relatively still apart from the trickle in from the growbed drain). Small pockets of higher-concentration ammonia wouldn't bother larger fish but to a little fingerling it might be toxic. As I said, long shot...

Another thing is that our pH test kit only goes up to 7.4 and so when I said "7.4 to 7.5" I should have said it was pretty much at the limit of the kit. Another long shot, but if that indicator (bromothymol blue) is only useful over the range 6.2 to 7.4 (the range on the card that came with the kit), then who knows? We might have a pH of 8 or more in there, and suddenly the 0.1ppm ammonia is toxic to the fish.

May need to invest in some more hi-tech test kit.