Backyard Aquaponics
A place to discuss aquaponics

Hello Everybody,

I have an outdoor EPDM lined pond holding apporx 25,000 litres. It's been filled for 8 months. (Initially with bore water - but 5-6 "test" goldfish were struggling after some weeks and I had to replace water with rainwater and that was about 7 months ago).

Since then have had approx 40 goldfish - they were thriving - many, many babies seen in the last 2-3 weeks.

1 week ago I received 100 silver perch fingerlings - arrived in good health and seemd to be doing well - feeding (crumbled supplied by fish supplier) etc.

2 days ago I introduced 3 new plants (from Bunnings) which I had to bed into some rocks crevices which I filled with leftover topsoil from a gardening project - probably 5-6 shovelfuls.

Yesterday, the silver perches seemed to be grouping at the pond edge and seemed sluggish. Today they started coming to the surface - seemed to be gulping for air and then started dying. Now the goldfish are doing the same - surfacing at the pond edge. I noticed soon after my plantings, that the water was quite dark and now it's worse - almost dark brown black - I read somewhere this may be a sign of low oxygen.

My test results - Ammonia: 0ppm, Nitrite: 0ppm, pH: 7.5. This is my first test so I don't know what previous levels were.

My reaction: 1. Raised the height of water flow (approx 4.000l/hr) from a small scoria bed/ gravel stream (which was gently flowing constantly onto the surface of the pond - my idea of a biological filter) to introduce some aeration. 2. My 15 minute/ hour pump (approx 3-4,000 l/hr) to a grow bed was turned to constant on so the water flow (and presumably aeration) is increased fourfold. Instead of adding salt - it would have involved a large amount for the pond size, I am presently overfilling the pond with bore water which is moderately salty (but would have other trace heavy metals).

Is it possible the topsoil upset the system?

Any suggestions before I have a total fish holocaust?

Thanks. (What a Christmas day!)

Though I do not fully understand how much growbed filtration you may have. If everything was looking okay before introducing new plantings I think that maybe there could have been fertiliser in the plants and I would be curious to know what was in the soil mix/ potting mix. If it changed the colour of your pond water it is leaching something. Pictures always help us to make more of an educated assessment, good luck anyway!

Introducing 100 small fingerlings (and they must be small if you're feeding a crumble)... wouldn't have been responsible for any significant oxygen depletion in a pool that size...

Whatever was in that top soil must be responsible... I'd remove it immediately...

I'd also remove the fish if possible... into a highly oxygenated tank...

Then drain down the pond... at least 50%... and refill with, preferably, rainwater... if not then the bore water... adding any form of additional oxygenation you can...

My concern with the bore water is the fact that you previously had fish "struggle" in it...

If you can't remove your fingerlings... then, sorry... I don't hold much hope for them...

Good chance that the shovel fulls for top soil and the potting mix from the plantings are playing havoc with your water. Such things can have lots of organic material in them as well as the microbes to slowly break them down but now that you have put them in your water, it sounds like they have exploded out and are breaking down other organic matter that was in your pond and very likely using up all the dissolved oxygen.

Get an air pump and air stone of an appropriate size for your pond and get it running ASAP or add in a fountain or waterfall pump at least temporarily to turn over more of your water each hour.

Pond 25,000 liters and only 7000-8000 liters per hour of pumping isn't really enough when problems come up. For an aquaponics system we usually suggest pumping the water volume of the tank over each hour. Heck, even for ornamental ponds I think turning the water over each hour is recommended.

Adding dirt into a system is like adding a huge bio-load to the system at least temporarily. this is probably why most people will recommend not adding dirt/compost into a system and washing the dirt off the roots of store bought seedlings. It might not be as bad when the plants and dirt traces are in the grow beds but placed right in the pond, most people would recommend using soil-less growing media in the future, like gravel. Most pond plants don't need soil and planting in gravel is fine.


Add as much aeration as you possibly can. Perhaps try removing as much of the soil/dirt as you can but the damage there is probably already done.

Septic tank airators put out a lot of volume if you have one on that system, borrow it and follow Rupes advice get the soil out and change water.

Microbes in the soil is what depleted the oxygen in the biodome causing it's first failure.

Agreed, would not have been a problem if there was a lot more bio-filter.

Thanks all.

Bad and good news.

Most of the silver perch fingerlings didn't make it through the night - I think I saw maybe one or two this morning (out of 100). Many carcasses littering the pond base - ouch! that hurts!. Interestingly some locally caught pygmy perches are still happily swimming around.

Thankfully goldfish (including their many babies) look alright. In fact they were happy enough to feed this morning (not 12 hours ago!)

The bore water was running all night - pond just overflowed. I think the 4-5 "test" goldfish in the start up period were struggling as the pond chemistry had not "settled" adequately - the pond is beneath some eucalypt trees and leaf dropping is an immense problem (only partially solved by my own makeshift leaf skimmer system) - and I thought perhaps the decomposition of this might have been responsible for the oxygen depletion in that initial borewater period. Perhaps this was also a factor but just the sudden change following my introduction of plants and topsoil may have triggered something awful.

Here is a picture of the pond in its construction phase. I've since added a cattle trough (3m long X 0.5m wide X 0.4 deep) filled with black scoria as a grow bed - filled to brim over 15 minutes then drained by gravity each hour) which hasn't done well. I thought insufficient fish in the pond to provide the nutrients (only 40-50 goldfish till last week's 100 fingerlings, now back down to 50 goldfish). All plantings in the grow bed died over a matter of weeks. Also I have a small scoria filled "stream" taking the water from the skimmer - which is merely an appendage to the pond in which sits a constantly on pump.

The pond volume is actually 15,000 liters (sorry typo yesterday). As this is an experimental outdoor "natural" system, I have had to make things up as I've gone along - I'm sure the ratio of pond volume : grow bed : fish supported is all not to established formulae but I have variables that conventional systems don't eg, the leaf litter, plants in the pond itself etc. Can anyone make any recommendations?

I will post some updated shots of the system later today.

My thoughts now are to 1. stop the bore water - don't want it to fully replace the rainwater. 2. slowly re-establish the grow bed filling and stream systems 3. get a large volume air pump when the shops open tomorrow.

Any suggestions appreciated!!

The cattle trough must not be filled to the top, the top 1 - 2 inches must remain dry. Or the plants will die.

If you have a spare pump lying around, put that in the pond just spraying into the air, this will provide a heap of circulation and aeration.

Once we see the current layout of the system, I am sure we can come up with some ideas to better filter your water, without ruining the aesthetics of the area.

Some update pictures

More pictures

Some comments:

Re: filling of external growbed - the water gets to just cover the top of the scoria then drains. Is that excessive?

Re: topsoil removal - decided to leave it as is - I had covered the top of the soil, around the base of the plant, with pebbles so it is more or less "sealed". Any further disturbance would only release more soil into the water. What was hard to avoid was the spillover of the dry sandy/loamy mix into the water when I attempted initially, to fill the planting cavity.

The reason I decided to use soil - the pond plants weren't doing very well - just wasting away. I thought the soil would allow some nutrition to be avaiable to the root system, but a part of this must have escaped into the warm water (temp in the mid 20s C over Xmas) prob causing a bloom of microbial activity.

It would seem that the whole system, despite being 7 months old, is still relatively immature from the biological perspective. 1. the pond plants don't seem to freely get their nutrition from the water 2. the external grow bed isn't able to sustain anything yet 3. the system seems to have destabilised with a seemingly minor "insult".

Interestingly the only fish that have died are the recently introduced s.p. fingerlings. Perhaps they were raised in an ideal environment and were the first to suffer from the drop in oxygen? Or perhaps recent move stressed them so they were more susceptible. I thought they were a hardy species...?

Hardy speies and a species able to cope with ALL the wrong things ..... not same thing.
Mate Merry Christmas , but learn the rules or da fish gonna die , and the fish ain't to blame

Sorry to hear about your disaster...

To avoid future disasters, I would suggest that you post your intended actions onto this forum and ask for comments before going out to do it. Step back 5 by 5 as what the safety reps call them... Take 5 steps back and take 5 mins to think or ask the question...

Intentional adding of soil is usually avoided.

The reason why your pond plants aren't doing well is probably because there is not enough nutrients being produced from the nitrogen cycle by the goldfishes. What are your water test readings?? Ammonia, Nitrite, Nitrate, pH.

I think I would not being stretching myself to say that all of us on this forum have grown plants without any soil added intentionally to our AP systems, apart from those loose bits stucked to the roots of seedlings...

Spend some time on the forum reading and learning from queries posted by others. It is recommended that for growbeds, the filling of water should be no more than 3cm from the top of the growing media... So in short, if you can see water when the beds are full, then it is flooding too high...

Also as a minimum, from pond websites, it is recommended that you turnover your water once every two hours. The water also needs to be passed through filtration that is sized to filter the water volume. From an AP perspective, it is recommended that water is turned over once every hour and the filtration is sized suitable for the fish load. Note that how many fishes you can have in a pond is not determined by how much water you have but how much filtration you have. I don't think that your existing setup meets the basic requirements.

Also goldfishes are usually more forgiving to the shit you throw at them. So if the goldfishes are surviving alright, it does not mean that the system is alright... And while you are having problems with the system, stop feeding them. It is the No. 1 rule.

The newest fish added to the system are likely to be in a weakened state from the transport stress. Also, I believe silvers like kinda hard water so the rain water in the system before the change may have been stressing them further. Then between the microbe cloud sucking down their dissolved oxygen and then change in water back to bore water being another stress.

Most fish don't like sudden changes so different pH, temperature, and water hardness from a water change can be a far more drastic change than we realize and should be done carefully.

Ok, your existing system. The black scoria bed. Make it so the top of the scoria never gets wet. Flooding over the top of the gravel is probably what killed your plants, not the lack of nutrients. Also, the black scoria probably gets really hot for small seedlings in summer. Get some shade cloth up over that bed to help new seedlings get established. Once you have a good leaf cover from plants growing in that bed, you might be able to take the shade cloth down.

An ornamental pond is a different creature than an aquaponics system and finding the right balance to try and combine aquaponics with one can be tricky. Even for an ornamental pond, you want lots of water flow and aeration though. If you can't increase your pumping and build a splashier waterfall, get an aerator and air stone going. A fountain going in the middle of the pond might be effective but the pump will probably need leaves cleaned off it all the time so an air stone down in the deepest part will probably be more effective for less electricity and trouble.

Here is a rule of thumb about amount of aeration per a given volume of water.


So for a pond the size of yours, I would suggest as much as 270 liters per minute from an air pump with big enough air stones to handle that much. You might not need so much but I'm sure a septic system aerator could handle what you do need for a reasonable amount of money.