Backyard Aquaponics
A place to discuss aquaponics

Hi guys been on here for awhile hiding in the shadows ,

I'm running a basic ibc system flood and drain for the last 3 months, plant growth is amazing and even fish growth has been good, the one problem I'm having is I have been losing fish and about 1 or 2 a week for the last month or so.

In the last week though I have lost about 8, I had put it down too a recent cold snap that we had but just want a few opinions any help is great

All my test have been pretty much the same no spikes to speak of, test from tonight were :

Ph 6.4
Ammo: .25ppm
Nitrite 0ppm
Nitrate 0ppm

Thanks in advance guy and girls, please ask me any questions to try and help

Cheers Alex

No spikes? How about in temperature, that could kill them. What is your water temp at 7am and 5pm?

I'm no expert on Murray cod but from what I read your ph might be a bit low generally they do better in the 7-8 range. 6.4 is fairly acidic.

i cant imagine 6.4 killing fish like that, but i am an absolute amateur at Australian natives. I would say the problem lies elsewhere, possibly disease. Take a picture of recently dead ones or even better moribund ones.

Whats the temp aswell? give us as much data as you possibly can.

pH seems unlikely but possible.. keep in mind that the ammonia becomes more toxic as you raise the pH. Probably not a problem for you with the low temps though. I wouldn't adjust the system pH itself at this point, I'd be looking for other causes first. If you do finally decide to do something with the pH, adjust the top up water only and make it gradual.

How large are the fish and how many do you have?

I'd look and see if there is a dead fish that's been missed and is still in the system (they don't always float right away).
How cold did your water get and what's the norm for this time of year there?

Do you have much algae? If you do then Dissolved Oxygen levels will fall at night and this could be killing the fish. Also pH levels will fluctuate during the day and because the algae respire at night producing CO2 the pH will go down overnight. Check your pH in the morning if this could be a problem.

pH 6.4 is definitely not a problem, my system is running in the range of pH6.3 - 6.6 with Murray Cod.

If it isn't a high diurnal temperature fluctuation problem, do they have white spots on them?

No real algae to speak

Have a Venturi running of the pump as well as the drain from the grow bed which is running on 15min on 30min off 24/7

As for white spots haven't seen any on any of the victims

Going out today to get a thermometer for the tank and will add readings ASAP

One victim

I reckon starvation, the same thing happened with mine due to them not being pellet trained, I wrote about it in my system thread early this year. The hollow stomach area is the indicator.

That was my thought to start with but the do take pellets so unless it's just the smaller ones getting bullied out of feed by the bigger one, I also chuck in the odd earwig as well which the eat too.

I started with 45 and now down to around 30 don't really want to lose anymore if I can help it

I feed them at night time when they are much more active swimming at all different heights in the FT and they are very active when they feed some taking from the service some in the middle and others on the base

I'm feeding at about 2 teaspoons a night and there is always some residual feed left over, which I clean out bout once a month because of the fear of ammo spikes which haven't happened

Get some bloodworms from the pet store. Try them on them, you might need to wean them onto the pellets.

They are happily taking pellets so not worried on that side of things, I'm thinking maybe it's just the bigger ones chasing the smaller ones off the food

looks like disease to me, see the blood on the underside of the eye, most systemic bacterial infections present exactly the same way in salmon.

Would also be a bit of bulging to the eyes aswell?

i dont know much about australian natives, but it looks exactly like yersiniosis in a salmon.

thats my guess.

Now you have to figure out what is causing them to be stressed enough to break out with it, in salmon its usually water getting too warm or dirty water. Once you fix whatever is annoying them it should sort itself out.

I'm not saying it's not what Gmturner suggested, I'm not great with fish diseases, but I know some of my cod managed to be weaned onto the pellets, and they are growing nicely, then there are those that didn't manage it, and they didn't grow and seemed to die of starvation. They are very skittish when they are small, and the bigger ones bully them into not coming out from shelter, and hence they never managed to get weaned.

Is it only the smallest dying, or is it a range of sizes?