Backyard Aquaponics
A place to discuss aquaponics

Hi,

I've started to have a few fish die on me. Two yesterday and two more this morning.

My system is a 3000l tank with 3 1000l growbeds on flood and drain.

The system is over a year old closer to two.

I'm stocking silver perch.

Testing shows:
Amonia 4ppm
nitrite 0ppm
nitrate 0ppm
ph 6.4
temp 16.5

The thing that worries me is that there is no nitrite.

Is it possible that at ph 6.4 possibly a bit lower but not 6, that the bacteria colony has crashed?

I had previously salted about 4 months back when there was a power failure and amonia and nitrite went very high.

Before having taken the reading I had fed the fish (which I'm guessing is a bad idea) but they are feeding strongly.

Should I be cutting food and trying to buffer the ph up a bit? I could do a partial water change but it would be with Sydney tap water which is clorinated.

I'd appreciate any suggestions as to the best way forward?

Yes, stop feeding your fish, don't bring your pH up yet, having a low pH while you have high ammonia is a good thing, wait till your ammonia drops a bit before bringing it up. But silvers don;t like low pH, you can generally see a change in their behavior when the pH drops down near 6. Partial water change won't do any harm, even if the water is chlorinated if it's only something like a 25% change out. Salt can't hurt, you have probably lost some salt from the system after 4 months. How many fish are in there?

Any feed or muck on the bottom of the tank, dead fish behind pump etc??

If the fish were all alive and thriving before, and now they're not, then obviously something has changed; the first trick is to figure what changed, the second trick is to figure out what to do about it before everything dies.

It's possible the fish deaths have nothing to do with anything, then again, it could be something? Do a necropsy and look for anything suspicious. You might get a better indication of what's wrong in your system by looking at the fatalities than looking at the survivors and their environment?

Stop feeding the fish for a couple of days, aerate well and/or pump continuously, then test the water again. I'd not play with pH as 6.4 is still within "range"; whether or not the bacterial colonies have 'crashed' is dependent on what the pH was a few days ago and if there was any sudden change in water quality.

If you suspect a parasite or virus, salt to 3-5ppt (3-5kg unadulterated pool salt per 1000L water) and do whatever you can to keep the system temperature "high" but more importantly, stable.

Sydney had some recent rains, any chance of run-off contamination? It's Spring, got any neighbours getting out into their yards for the first time in a long time and spraying all sorts of who-knows-what? Have you noticed any increase in bird-life in your area? (Some bird poop can contain nasties, if they shit in your system...)

How many fish? Have you changed feeds? Is this a new bag of feed?

[Joel got in first... ]

At that pH and water temp, 4.0ppm of Ammonia definitely isn't toxic to your fish... it would actually need to be in the high 20's to be harming your fish... Google "Ammonia Toxicity Chart Ecofilms" and you'll see what I mean.

What you do need to address is the fact that you have 4.0ppm Ammonia. I think it may be the case that the Ammonia is a side effect of having dead fish in the system that have died from something else. It could also be that you are overstocked, how many Silvers do you have and what is their average size?

As far as the bacteria colony crashing, my system runs between 5.8 and 6.5 and has been down to 5.5 a few times when I haven't had time to check it for a few days. On a couple of occasions it's even been down to 5.3... and the bacteria colony hasn't crashed yet. The Silvers do start going off their feed at a pH of 6.0 as EB pointed out, and they stop feeding completely at 5.8... so you'll know if your pH is getting down into danger territory and risking a collapse of the bacteria colony... but it really needs to get down to around 5.0 for that to happen (I had it happen in an aquarium recently).

Nitrite conversion to Nitrate happens very quickly, so in a system with a healthy bacteria colony you normally don't see any Nitrites in your tests, even when you have constant low level Amm readings.

Do you have a stand alone aeration system in the FT (ie: not a spray bar run off your water pump) that will operate during a power outage?... Have you had a power outage recently?

Or just look at it on BYAP, seeing we created it and he pinched it...

Thanks everyone for the replies!

Before it was suggested that I do nothing I had added some dolomite to the system, only around 3 handfuls.

I also added some coral I had around in an old sock in to the ft. I was hoping this may act as a bit of a buffer going forward.

All this has made no appreciable difference to the ph.

Amonia is possibly a little less tonight although it's hard to tell.

As for runnoff it's unlikely as the tank is in the ground but about 20cm above ground level. It may be possible that birds have shit in the system but again not super likely.

I can't tell if there is anything on the bottom of the tank. I'm blind so can't see but my wife tells me that the she can't see down to the bottom (aprox 1.1m deep).

The tank has always been like that though never crystal clear.

I do have additional air pump although not a battery backup one.

We did have a power outage for about 1 or 2 hours a few days back. Perhaps that is the cause?

As for stocking density I've got aprox 95 silvers. They range in size from small (say 5cm) to about 15cm I think. Probably stocked too high?

I had been intending to send some off to a friend when temps warmed up. Maybe I need to get that moving.

I guess at this point I'll just keep monitoring.

If any more fish die I'll get a photo taken and upload it.

With 3000L of gravel you've probably got around 2400-2600L of wet gravel in the system, and Silvers require 20L+ of wet gravel per plate sized fish (about 30cm)... so you're not overstocked, you're system should realistically be able to handle 120 plate sized Silvers.

Are you getting a build up of fish solids on the floor of your FT?... I siphon the waste off the floor of my Silver's system every week and do a partial water top-up with aged tap water. If your system has been running for a couple of years there may be quite a build up in your FT, that would definitely lead to high Ammonia.. even more so if there is any uneaten food also settling in the FT.

If your tank is partially buried you can still siphon the floor using a siphon that fits onto your garden hose and is powered off water flow from the hose. I haven't used one, but supposedly the tap water that drives the siphon doesn't enter the system.

Hi,

I made an error with saying my gbs are 1000l. On further thaught they are actually 600l which will significantly reduce the carying capacity of the system.

Still, my fish are rather small and I think from calculations that I should still be ok although probably should offload 20 or so pretty soon.

Does that sound about right?

With respect to siphoning the muck out of the ft, will disturbing the sediment possibly make the problem of ammonia worse?

As before I'd be literally doing this blind . I could get the siphon and move it around on the bottom of the ft and hope for the best .

Or is it sufficient to just leave it in one place and hope that I get all the muck?

There were no more dead fish this morning which is a start.