Backyard Aquaponics
A place to discuss aquaponics

Okay, there will be some who hate me 'cause I've got a huge tank that I can use, there will be some who think I'm mad for considering it, there will be some who think I'm mad for not considering it…

Is a 14,500 l tank too big for a fish tank?

The story so far:

The medium tank option:

I'm hoping to be able to get a 1,800 l poly rainwater tank for $200 – a second – the roof has collapsed on it but it sounds like it will be okay for a fish tank – haven't seen it yet…

Medium tank details:
Diameter: 1.38m
Inlet height: 1.43m
Overall height: 1.50m

There could be other seconds available, but this one sounds like good value…

Growbeds
I was happy with the idea of building a system based on this size tank with 4 growbeds made using treated pine and pond liner ~ 2.4m x 1.2m x .3m ~ 860 l each.

So that would be a 1,800 l tank with 3,440 l of growbed. Getting close to the 'perfect' ratio (~1:1.9).

Stocking
I'd expect to stock initially with 50 Jade Perch, and then at about 3 months add another 50 Jade Perch. Depending on the growth rate and system capacity keep the stocking rate at about this level if things all look good.

Assuming growout in 9 months that would give me about 150 fish at any one time and a fish every 2 days… This would be close to perfect for our needs.

[This works out at about 50kg of fish swimming in the tank or about 28kg of fish per 1,000 l ~ 50 x (0.6 + 0.3 + 0.1) - in reality I'm sure it would be less.]

The big tank option:

I have a 14,500l tank that could be used instead of purchasing the smaller tank because we have just added another larger tank which should be enough to cover our water needs.

Stability
Reading about other large systems it appears that they tend to be much more stable etc. even with relatively low growbed volumes.

Pump
But, I'd need a larger pump, which would consume more power, which we have been working hard to reduce to a minimum over the last few years (solar panels one day...).

Water
If I had to exchange water for whatever reason, it would significantly impact on our main water supply. We only have rainwater tank supply.

Access
It's a bloody big tank that sits high of the ground so would need some decking for easy access. How the hell would you catch the fish (yes Jayme I have a cast net, but...I can't see my DW gettin' in the tank to help).

The big tanks details:
Diameter: 3.09m
Inlet height: 1.91m
Overall height: 2.2m

Good stuff
I could stock more fish and give/barter them away.

I could add more growbeds and give/barter the veg. away.

I guess the tank could be only half filled with water, but then I'd most likely be looking at having to have 2 pumps…(gravity = height/fill level)

The both option:

I could start with the smaller tank, making sure I position the growbeds such that they could be hooked up to the larger tank at some later date...

What would you do?

Any comments, corrections, hate messages, praise etc. welcome.

If you reckon you have the growbed space for later on, go the big one - more stable etc as you said, and I would have it full of water so one pump.

Catch the fish with barbless hooks

All of the above.....

Even if you start with the smaller tank, you can always turn it into a sump tank later on....

Enough growbed capacity to start with either even if you add the large tank in later... just stock to the capacity of your growbed volume rather than the "big" tank volume....

To get a sense of stocking, growbed capacities etc.... see Jaymies thread... she's got a big tank

That's not too big! Yes I'm envious but who could hate you for having a great tank?

I would probably bury it in the ground if it were mine, short work for a backhoe but a dang lot of shoveling

Don't let fear hold you back go the big tank

You've got it right I think gnash, it's fear that is holding me back. Plus a lot of unknowns that I guess I'll find answers to if I keep reading this forum

Rup, I think this is one of those unknowns for me. If I go for it with the big tank and only start with 50 fish (fingerlings), and a couple of grow beds, I just can't get past the idea of having to turn over so much water to supply enough nutrients to the plants.

Having to have a big pump does not sit well with me, but if I gravity feed from the tank, and just pump back from a sump the pump may not have to be as big as I think...but then the whole 'getting nutrients to the plants' question comes back again...

Check

You only need to turn over the volume of your growbeds every hour or so......not the whole tank.

This is what I can't clearly see. If I only do that the nutrient level in the water would be so much less than a smaller tank system...will the plants get enough nutrients to grow?

Maybe the penny just dropped. It will just take a whole lot longer for the level of nutrients to build up, but they will get there eventually...

Added:

And I guess provided I can get the poop onto the growbeds, all will be fine...

Ding

Thats why a bigger tank is more stable

It's all good

If I had that tank partially buried in the ground with the top just a little lower than the height of my growbeds, I would either run a 2 inch airlift up from the bottom center a couple of inches to just enough height so that the airlifted water & poop solids could gravity flow to the growbed(s) and gravity flow back to the tank, where the inlet to the tank was set at 90 degrees and might gently circulate the water column. Would take a pond aeration pump to get enough air to make a good airlift at that depth like my Dolphin pond pump @ $134. US might work ok.

My other option would be the same type setup, just using a regular water pump with enough capacity to run excess to circulate the column and cause solids to settle out in the bottom center where they can be sucked up.

Thanks OB1

I should be able to add the fish with minimum growbeds to start with and let things build up a bit. Then add growbeds as needed...