Backyard Aquaponics
A place to discuss aquaponics

Hi, I just joined up on this forum since I am getting interested in aquaponics and i could really use some help with figuring out the stocking density for my pond.

I have a 8000-9000l pond in my garden it contains a fountain with a large flow rate of 30,000 lph water falls from 100cm above the water surface.

The waterfall contains a small bog filter aprox 0.4 cubic meters of gravel is in it. I have several pond plants in the bog but the surface area of that is only around 3-4 sq ft

I have a shelf 20cm wide and 4m long around the edge of the pond filled with baskets containing gravel and pond plants.

The pond is longer than it is wide and has extremely strong current I have 20 small gold fish in there at the moment and they love it, when they stop moving to eat you can see the current dragging them backwards. ( they have plenty of places to hide where the current is not as strong)

I would like to stock a few fish species in here not to eat but a personal hobby of mine as I want to get them to reach maturity to see if some day I can breed them.

Mainly trout, perch, and bream.

I have enough room for one decent sized grow bed 75cm wide 2m long to compliment the plants I currently have. The only space I have for this bed is in the shade though unfortunately so i think that would have to factored in. I don't care what plant is in it as long as it filters the water for my fish so any plant that would be good at taking out a lot of nitrates would suit.


Currently my water quality is excellent with maximum DO and 0 ammonia 0 nitrite and 10ppm nitrate however all my pond plants are nowhere near mature yet and the goldfish are still small.

I'm struggling to find the best way for me to go about this as I've read that 1 sqft of grow bed per 1lb of fish. The fish will eventually be a lb each or more so that would mean based on the space of the growbed I can provide I'd be stuck with a maximum of just 15 fish?

Anyone's input or idea on this would be great thanks

You can make some allowance for the plants you have there growing already, plus some extra for the fact that the system is so large, bacteria grows on all surfaces, and I would think you can push it up to 20, perhaps 25 fish without too many problems.

Thanks for your response

I was hoping to keep 50-60 fish but I guess that's probably impossible.

Can you recommend anything I could do to push that 25 fish up slightly maybe to 35/40?

Maybe a sand filter? Should provide a good amount of surface area for the space it occupies...

Also, if the fish aren't for eating and growth rates aren't too important then a lighter feeding regime might give leeway for fish numbers.

Why don't you stock with 50 odd fingerlings, keep an eye on levels, and when they get bigger and the system is under pressure, remove a few for the plate. Some may die off from natural causes too.

How big of a barrel do you recommend is need for this sand filter?

Also what about all the nitrates sand filter wouldn't contain plants would it.

I thought I could feed less but i read somewhere it's inhumane not to feed the 2% their body wieght?

If it's ok to feed slightly less I will do that

would be handy if you can provide the dimensions (L x W x Dep or radius) of the pond...
If you are 0.5m deep then you have equivalent of 16 half IBC's for 8000L...thats a lot of FT...
(I am guessing you are not 1m deep, but even 4x2 = 8 full IBC's = 8000L is a lot of FT)

#1 - you have a pond not an AP system or aquaculture tank - so a lot of the rules/guidelines don't apply or can generally assumed to be 'worse case' - large volume systems are typically a lot more stable..

#2 - you mention steps around edge etc - then simply increase your plants within the pond, reeds/pampus grass/sedges/papyrus etc in pots.

#3 - in a fully fledged pond there will be a lot for the fish to eat. Particularly goldfish. You could feed them 2-3 times per week and they wouldn't suffer. Keep in mind you will have algae, insect larvae, and all sorts of things in the water they can eat. Also you can add some duckweed and valisneria. You will know if the goldfish are hungry cause they will eat it all, in most ponds I am familiar with of that size it rarely happens.

Feed will then increase depending on fish species, ability to feed as an omnivore, and number. Most quoted rates are for growth not sustaining, so there is a lot of leeway.

#4 - if you want to breed then better you keep the numbers low anyway, 25 fish is quite a lot *but* the flipside to the equation is you have >300L per fish, so 40-50 would be achievable provided you had a reasonable setup.

However it is unlikely you could have the mix of fish that you describe in the one pond.
With things like the trout then management and stocking rate would be a much greater issue and numbers will be limited as EB notes. If you went that path then your pond would have to be better setup for it.

#5 - unless you want vegetables then you can feed water over just about any plants. You are then not restricted to the limitations of vegetables. And you can maintain mature plants.

#6 - I wouldn't worry about a sand filter - it will just clog up with pond crap. If you thought you really needed something fill a 200 Litre / 40 Gallon drum with 2-3" sized gravel/rock. Feed water to the bottom and overflow out the top with a false floor that you can flush directly with a tap/ball valve. You can easily wash crap down and out bottom when it gets too much. Would be miles more effective and give you some additional biofilering as well.

[edit] maybe be careful about the pampas grass - https://www.news.com.au/lifestyle/home/ ... 31f6d43a31

Dimensions are hard to get exact due to the shape.

I've attached my best drawing of the shape to help visualise

The dimensions are 4m long 1m wide at the narrowest and 2m wide at the widest circle part.

Depth is 1.2m throughout apart from the 30cm deep shelf all the way around the edge as drawn.


I don't plan to breed for atleast 4 years as I will be buying young fingerligs and most of those species don't reach sexual maturity until 2-4 years from what I've read. I plan to hopefully have another pond somewhere by then. I just want to start a breeding stock now.

I already have a gravel filter as in my bog/waterfall where I push water to the bottom of the gravel and it flows up through around 70cm of gravel then overflows back into the pond. It's only 3 sqft of gravel though so I don't think that's enough surface area for more than 3 fish.

I like the idea of buying 50 fingerlings and if they make it to full size and water tests show it's not coping I could remove some.

I do plan to cover the entire edge of the pond in plants and the bog but that would still only be about 0.8 sqm of plants do you recommend any long lasting plants that I could plant in a 0.75cm x 2m grow bed that could clean up nirates for me?

Thanks

Edit I can't upload photo on my phone

It's basically a large P shape

It's so strange I went out there today and the water is back to being completely 100% clear 1.2m down to the bottom.

It's doing well. I've got some more water irises on there way. And all the plants I put on the bottom of the pond are now visible again and surprisingly are doing great they doubled in size.

Can't wait to get my hands on more fish

If your only worried about removing nitrates and not growing crops you could look into biohome filter media it supposedly gets rid of nitrates aka a 'full cycle'and not just ammonia and nitrites look it up on YouTube try it myself on an aquarium, it's expensive but even if you get enough to just lower the nitrates or to increase fish stocking might be worth it plus doesn't run out.
Failing that just carpet the bottom of the pond with a carpetting plant, val I guess and get floating plants like frogbit water lettuce azora as well unless they eat they it eat it her, I know they eat duck weed

Letting a filter go slightly anaerobic will also release the nitrates and that's probably what's happening with the media mentioned above. If you don't clean it very often you off gas nitrogen as NO2. University of the Virgin Islands used this in their system by how often they cleaned their net tanks. I guess what I'm saying is that it's not dependent on using any particular companies media, just the conditions - anything that will grow bacteria will work as long as you can let it go without cleaning for long enough. You don't want the filter to smell bad (this is an indication that H2S is being produced) so occasionally clean it - when you do have to clean it, the easier to clean the better.