Backyard Aquaponics
A place to discuss aquaponics

Link to Galv / Zinc discussion:

http://backyardaquaponics.com/forum/viewtopic.php?f=8&t=4919

Nice work on the Zinc. Great to see some real science in action.
It would be interesting to run a control.
I'm thinking a small aquarium with a healthy goldfish and your tank water.
Just so happens I have one, with an established bio filter doing not much ATM.
PM if your interested in borrowing it.

Jimmy,
just talking about the sikatite, we painted the 10000L tank 3 times, the lid of the tank (3500L) 4 or 5 times (don't ask it was awful) and the corro bed (2000L) 3 times. There is still about 20% left in the 20L bucket.

I can't see how it will cost you $1000 to cover your fish tank

Given what you've got... I think the Sikatite paint is the way to go...

Coating the growbeds would be a snap.... the tank a bit more work... but easier and cheaper than trying to fit a liner... cutting/sealing the liner for the plumbing etc...

I've come to the same conclusion! I also think that whatever happens, I need to Zinc-proof the growbeds - that's a given, especially now that I am running some salt in the water - will be extra corrosive.

But as far as the 45,000L tank goes, I think my action plan could be:
1. Connect tap water to the AP refill point, shut off rainwater.
2. Divert rainwater pipe away from the rainwater tank
3. Drain the tank over the next couple of months (step up the watering campaign on the veggies and fruit trees)
4. Give the whole inside of the tank (apart from the lid) a couple of coats of Sikatite

This actually sounds highly achievable and relatively inexpensive.

have you thought about condensation on the lid of the tank is this going to be an issue ? if it is then i would paint it as well or add some vents or something

Cheers
pete

Good point. Not a lot of use in putting all that effort in if the water still leaches zinc off the roof! Given that the levels of zinc need to be reduced by a factor of more than 100, we can't afford to leave any stones unturned...

Okay, second batch of goldfish were doing well. Emphasis on "were".

A couple of days ago I pulled a dead one out. Tonight another one looked very unwell. Swimming on its side at the top of the tank.

So far over the past week:
Ammonia: has been dropping. Now reading zero.
Nitrite: no reading yet.
Nitrate: increased to 5ppm, now reading zero.
Temperature: 20.5 tonight, has been up to approx 23.
pH: Has been increasing. Tonight it was 8.0 !!!

The most urgent thing appears to be pH - nothing else seems to be running at problem levels at all. I've put in some more "pH down".

The only other thing is that I've shut off the inflow from our rainwater tank (will plumb in a mains connection this weekend), so the concentration of salt etc has probably been increasingly slightly as the evaporation takes H2O out of the system and leaves other things behind. Still, I'd be surprised if the water volume has decreased by more than about 5-10% this week.

Any thoughts? Could be the big "Zn" of course.

I paid a mob to test my water for heavy metals, cost me ~$70. If your buddy at the Uni is too slow, give 'em a call!

It might actually be the pH fluctuation that's stressing your fish - is there lots of algae in the tank(s)? Or temperatures - What kind of temperature shifts do you have? Measure first thing in the morning at 4-5pm. I think it's anything over 5 degree change stresses 'em out.

Could also be overfeeding (as in rotting food on the bottom) or a dead fish stuck in your pipes or something like that. That bacterial action on dead things does bad things to the water apart from ammonia.

Do the fish look healthy apart from the discolouration? No fuzzies?

What does Zn actually do to the fish apart from concerntrate in them and thus become unhealthy for us to eat? I know Cu and Ni inhibit the immune system (or attack the liver) - is this all heavy metals?

From the little I know, all heavy metals have similar effects on us, even gold. I'd imagine it's the same for fish.

Read your other thread... got it tested already.

I got 20ltrs of rubber pant to seal some skylights and it only cost $100 ish. Went on like tar but turned to rubber when it dried. Not sure if its fish safe but it is used on tanks.

Have to look up what it actually does to cause death in fish... but concentration follows the order... liver > kidney > intestine > gill > muscle ...

Lethal in some species from as low as 4mg (Zn)/L.... with Rainbow Troutound to be one of the most sensititve species...

Temperature increases toxicity... primarily because it also increases fish metabolism...

The little guy didn't make it. Fished him out this morning. He looks really weird.

If I had to guess, as a layperson, I would say this fish ate itself into oblivion. I mean, look at it!



Is that an issue with overfeeding? Can they overeat to the point of dying? Or, perhaps this could be down to a change in temperature - it eats loads when the water's warm and then it cools down and can't digest it?

Temperature now (8:30am) is 18 C, so it cooled about 2.5 deg overnight.



Can you please let us know where the 4ppm figure comes from? The aquaculture sites recommend maximum levels of around 0.01 ppm but that could be in a "better safe than sorry" (important if you're investing $50K in one year's worth of fingerlings) so it'd be good to know what the "fingers crossed" range is in the backyard setting...

The problem appears to be some form of 'Bloat' not unlike 'Malawi Bloat' common to a lot of African Cichlids.

Before I say anymore a few details would help:
NOTE: Other species of fish are prone to similar problems.

1. What type of fish are you keeping and are they all 'Virgin' stock?
[By 'Virgin' I mean, have they ever had any contact with other aquarium fish species like maybe a goldie that was once inside in a tropcal tank etc?]

2. Did or are the fish feeding less [or not at all] compared to usual?

3. Have there been any sudden changes in the fish environment?
[e.g water changes, pH spikes, or any new fish introduced etc]

Hope you get this sorted out, please get back with the answers and I will then see what I feel the problem is.
[No I am no expert but having been a keeper and breeder of tropical fish for more years than I can remember I do have some knowledge in this area ]