Backyard Aquaponics
A place to discuss aquaponics

That's good to know that it was just a mechanical issue (of sorts) and not to do with anything related to how your setup is running. Although it sucks hard to lose that many fish, it is a relief to be able to pin down the problem.
Best of luck with the remaining fish!

Would have the electricity caused the problem?

I'd have thought it'd have taken out all of them if that was the case? And I didn't think they'd earth enough inside the water.

I remember seeing a few people talking about how their pumps were shocking them, but the fish never seemed to die (from what I remember anyway). Your fry might still be in a more delicate state due to the age though.

My marine tank has often shocked me but never the fish.

You should always run any AC powered water pumps on a circuit protected by an RCD (all new domestic electrical installations have had to have them for quite a few years now). "Safety switch" type multi point power boards will do if the house doesnt have them. It doesn't take much to kill you (~30mA) if you have contact with the ground and an arm in the water.

The fish that survived may have stayed out of the highest voltage gradient area, the gradient would run from the live wire break to the least resistant path to earth, even if it is high resistance. Obviously it was high enough to prevent a standard fuse or circuit breaker to trip. In that case you may have had deaths for a different reason, if no backup pump in place.

hmmmm interesting, didnt think of that. Have never seen it happen in aquaculture, and we work with some pretty dodgy leads and have been shocked on more than one occasion.

There is one farm that i know of where they are situated is quite rural so the electrical supply is only single phase and apparently doesnt supply a ground return or some jazz so everything must be earthed to ground and as such everything on the farm has a charge to it, just touching tanks etc gives you a zap. They have just ordered a defibrillator just incase.

i know for research they do electro-fishing which is some pretty high voltages through the water and that only stuns the fish, they recover fine.

Was the zap quite sharp and painful?

Well it was a proper zapp! Not the kind of one you get when you take off a synthetic hoody:)
I had one hand submerged on a valve and the other (the one that hurt) on the frame of the growbed.

It's now over 36h with the grow bed loop connected to the fish without any loss.
Should be getting the water test results on Monday and will post them.

SWER (single wire earth return, is still used in remote parts of Tas. There are laws regarding how the earthing must be done, but I don't know the details off-hand. You shouldn't be getting zapped all the time though, so I suspect there is a problem with the earthing there.

The more that I think about it, and understanding the isolation of the FT to the pump tank, I can't think how the electric shock thing could work..
It would be like being inside a car with power cables on the roof... all safe until you touch the ground..

I would have wondered if the power leakage in the tank could have some kind of electrolysis that generated some low level noxious gas..

It's different if you get a tingle when you put your hand in the tank.. YOU provide the earth return, with the water in the pipes providing the circuit..

Eg.. is there any salt in the water that may have broken down to chlorine ..?
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Electric eels seem to make it work...

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I understand that electric eels pass a voltage from one body part to another and thus it's victim will need to be near that current path..

I would speculate that the motor's leakage parth would have been from the sump to the GB, where there would be the most likely earth point.. when you think of this possibility, you realise that the current leakage is from the windings and those windings are inside the pump that is still pumping the now contaminated water to the FT..

No one will likely ever know, but it is another possibility, and one consistent with electrical circuit theory..
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one of the workers told me its just too much power to dissipate in such a small area of earth or some such. They use quite a bit of power in a small area.

Sounds like poor conductivity on the earth stake- probaby needs a more extensive earthing system and better contact - more earth stakes and maybe deeper into ground that isn't too dry.

Just going back to this thought, remember that this is a suburban back yard, and the pump (was) likely a two wire (L/N) device..
It's a shame that Ben did not do some more tests to confirm the failure..
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Well I did a full water analysis of the day they died and had nothing at all standing out to be abnormal.
In fact it is considered save to drink!!
As in the pump, I have more respect for electricity and it's effects then knowledge in that field and did not want to experiment with the faulty one.
Since then I haven't lost a single one and they are happy surface feeding, growing and last measure was 53mm.
I have retraced all my steps and changes of the day before and couldn't come to anything significant. It's not easy to loose half your hatch and don't have a clear answer for why.

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