Aquaponics - Aeration

I'm planning on buying some trout in the next few days to grow in my aquaponics system, so I'm thinking a bit about my oxygen levels.

Toward the end of the trout growing period you have a lot of stuff acting against your trout. Your trout are big and make a lot of waste which depletes oxygen as it breaks down, your trout are big and need lots of oxygen, and your weather is getting warmer,  and warmer water doesn't hold as much gas as colder weather does.

You can test this by opening a warm can of beer, or waiting a few years and watching what happens when the oceans stop absorbing carbon dioxide as they warm up a bit.


I have a tube dumping water from my growbed to my sump.

This much water.

It's not under pressure, but is simply overflowing from the growbed at that height. ie this tube's height regulates the depth of the growbed.

no pressure

The tube stopped a few inches above the water and made some nice splashing and bubbling which I thought was adding some oxygen.

I'm probably quite correct in thinking that.

But then I added a tube all the way to the bottom of the tank, and pricked a few holes in the tube just after a narrowing where there was an elbow.

This sucks air into the tube via the Venturi effect.

Apparently, this is because the water experiences higher pressure at the restriction just below the elbow, but then lower pressure when the tube becomes wider again. The result of the low pressure is that it sucks in air.

Which is a little odd.

When you put holes in (or before) the bit that's actually restricted, the holes blow out water.

I know because I checked.

So the result is that oddly enough, air is drawn in and the flow of the water draws it down.

Even more oddly, is that the bubbles don't ever really come out. Some do when the water level is a little low, but these are very small, and not many.

The tube is full of bubbles all in chaos, churning around madly.

It looks like this in real life.

The bubbles enter at the top just where the clear tube starts, and they move all the way to the bottom.

Which is also odd given how gently the water is flowing.

At first I thought they were the same bubbles, but if you block the holes, they clear after a few minutes.


As far as I can tell the air is dissolving.

I have no idea if I'm probably quite correct in thinking this.

If gas really does dissolve in water that readily and in that quantity, it's no wonder fish can live in the stuff.

I think I just got re-interested in the world.

Perhaps it's because I stopped taking all those opiates for my hurty ribs.

120 Things in twenty years  thinks ribs make me less thinky.

[EDIT FROM THE FUTURE - I Thought I'd add a link to wikipedia's entry on Venturi and now that I've read it I don't think I have any idea what I'm talking about, but what I did clearly works. I'm just no longer sure why]

The shell grit seed raising seems to have worked.

There was some slight discolouration on some leaves that I think might be due to nutrient lockout because the pH is probably off the chart in that local area, but generally speaking, I think it works. The discolouration is not shown well on this pic. The true colour is closer to the lettuce leaf on the left.

When pH is at certain levels, various elements become less available. If your system sits at about pH 7.0 then everything is available.

I just lifted my first seedling out of the shell grit, and it had a 24cm root that came out in tact. I made no attempt to be gentle and just lifted it out. I tried another one and achieved the same result.

Anyway, no washing - not even a rinse, and three tiny bits of shell grit was all there was stuck to the roots.

I think I should have left it a little longer because there were hardly any side roots developed, but I planted it next to some existing established kale, so I'll have something to compare it with. The existing kale was planted around ten days earlier.

I add some seasol® from time to time, so I might add it directly into the shell grit once I see sprouts to make sure there are extra trace elements available next time. The slight discolouration might also be due to lower oxygen levels as the water probably moves quite slowly through the fine particles. I might sive the shell grit so I can get a slightly bigger particle size. I plan on reusing it for ever, so it's no big deal to sieve it.

120 Things in 20 years thinks raising seedlings in shell grit feels like a success

Aquaponics - Duckweed

Since I moved my duckweed into it's new home it's growing like some kind of thing that grows a lot.

It looked like this nineteen days ago.

Then eighteen days ago I lost a lot of it because I overflowed my tank and all the duckweed went for a walk over the edge.

It looks like this today.

It's not lost on me that this is a poor comparison.

I realise they look pretty much the same, but this latest one is many layers thick in most parts. The original pic is all a single layer thick. I had no idea it could grow this way in multiple layers.

I suspect this is a dangerous thing to grow on top of a fishtank as it might choke the water. I doubt  the water will see enough oxygen. If not for the fact that I only have one fish, I think there could be trouble.

I think I might scoop all this out and do a time lapse of it growing back, but then I think I might move it into some other containers or something.

120 Things in 20 years wants some trout fingerlings.

Aqaponics - Experimental tomato tactics

It turns out you can simply hack the top of a tomato off, stick it into your aquaponics system's media, and it will grow.

So as a bit of an experiment, I've been waiting until my big old tomato vine develops some flowers, then cutting off around a foot tall of the end growing bit with the flowers.

I jam it into the media and it wilts a bit. But then it comes good, the flowers open, and fruit is set.

It seems to be working, and might allow me to grow better quality tomatoes. I have no idea why, but it might.

It certainly will save some space.

Also it  allow me to grow six enormous tomatoes on a tiny one foot high vine which although it might not serve any purpose, it might look interesting. And let's face it. Looking interesting is what sells all those perfect little tomatoes still on the vine in nice neat rows that we see in super markets.

 My bee visited again today.

120 Things in 20 years is doing all those experements that don't really need doing so nobody else has to.

Aquaponics - Shell grit seed raising bee and gecko visitors

I found a little helper in my shell grit seed raising trial.

This gecko is tiny!

I also found a bee.

That's two now this year I think.

It left soon after I saw it visit my freshly transplanted wild rocket.

But my bee came back a little while later.

At least I think it was the same bee.

It certainly looked and behaved like the previous bee.

She looks busy.

120 Things in 20 years is now a bee keeper. I keep a bee.

Aquaponics - Transplanting weeds (wild rocket)

Sometimes I wonder what normal people might do if the weeds in their front lawn were getting so high that they were lowering local property values, but they were too delicious to cut down.

Our front "lawn" is made up entirely of weeds that we normally diligently mow to a controlled inch or so in height. This year, quite a bit of it is wild rocket.

Mowing the lawn swells amazing.

We've been enjoying it so much this year, that I decided that I should grow some in a more controlled fashion. Perhaps even in the new aquaponics grow bed. I'm not sure if weeds will enjoy the happy plant habitat of a constant flood grow bed. Even if they don't go into the grow bed, I'll at least grow it behind my shed or something. Somewhere out of sight anyway.

The problem is, the front lawn's collection is going to seed. I want the seed, but it's not quite ready to collect. So they are getting too tall and ratty to pretend they are simply between mows. That coupled with the fact that by a bizarre twist of circumstance, in the last few weeks, we went from a one car household to a three car household, all makes the front of our house seemed a little neglected. The natural habitat of cars you don't use is of course, the front lawn.

The result is I collected a bucket full of weeds.

And transplanted them to my aquaponics system.

It's quite an odd feeling seeing such fully developed weeds in an aquaponics system.

It might have been a first if not for the fact that a few years ago, I lovingly transplanted something that I thought was a lettuce, and even more lovingly watched it grow into a thistle.

I just looked up "thistle" and it turns out they are food as well.

120 Things in 20 years learns something new every day. (at least)

Aquaponics - Shell grit seed raising shoots

My attempt at raising seedlings in shell grit seems to have worked.

No real surprise there, because if it's going to fail it wont be for a while yet. The point of failure, if there is one, will be the plants rotting because the water might flow through too slowly, and become stagnant.

The shoots appeared this morning.

The lettuce and rocket have sprouted, but the kale is yet to.

I think it was only 4 days ago that they were sown.

On a slightly interesting note, the seeds that were directly sown to the growbed came up yesterday afternoon.

They were sown around 10 days ago. I figured they weren't going to show and moved on to trying the shell grit idea.

I still think it will be better to grow seedlings and transplant them just so you can space the plants properly. When you direct sow, you have to plant lots of extra and think them out because some don't grow, and some move around a bit and as a result you can get clumps of seedlings all in one spot.


So far so good with the seed raising in shell grit experiment.

120 Things in 20 years still has no taglines forming in its addled brain.

Aquaponics - Swirl filters for solids removal

Over the last few days, I've been reading a stack of stuff on radial flow and swirl filters.

Here's what I think I know so far.

As far as I can tell a radial flow filter moves the water in a very gentle manner, first down then up. The solids stay at the bottom. It often does this by having a container inside another container. One container acts like a bucket, and the other is mounted upside down from the lid. You add water and solid waste into the centre top, where it gently moves down to under the rim of the upside down container. The water then rises up to exit near the top outside rim, leaving the solids behind at the bottom. A tap is placed at the bottom so you can remove the solids.

I think I'm going with a swirl filter instead.

The swirl filter migrates solids towards the centre and the bottom, which should be the best position to remove them via a siphon. The path the solids take is a long one because the flow is circular due to the direction of flow on entry to the device. This allows more time for the solids to fall out of suspension (maybe).

So a swirl filter is a bucket with an inlet pipe mounted near the rim to introduce water and solid waste from the fish tank. The inlet tube is pointed in such a way as to make the water create a gentle whirlpool.

Normally, a tap is added to the bottom to remove the solids once collected.

As far as I can tell, a swirl filter changes the pressure of the water on the outside, making it higher than that of the centre due to it's rotational ... disposition.

This pressure (and depth) difference means that the top is no longer the top as far as the poop goes. The poop now thinks the top outside edge is the new top, and the bottom centre is the new bottom. So the poop moves to the new bottom which is right where I'l mount the bell siphon.

What all this means is that the poop is a little more committed to sinking than it's normal, only slightly sinking self.

It's also more likely to settle out near the centre of the bottom of the swirl filter.

Instead of using a tap mounted through the bottom of the swirl filter, I'll be adding an auto siphon in an attempt to automate the dumping of the solids into a worm farm.

Aquaponics - Shell grit seed raising

It seems like I've been trying for ages to find a decent method to raise seedlings from seeds.

My preferred method would be to just throw them all over the place and see what happens, but I suspect the clay ball media allows seeds to fall way down into it. It's possible that with the normal vibrations of city life, that the seeds fall all the way down into the water and then sink to the bottom and rot.

One problem with raising seeds in potting mix is that you do a lot of damage to the roots when you wash them before transplanting them into the aquaponics system.

I add shell grit to the system as a pH adjuster. The nitrifying bacteria tend to move the system toward the acid side, and the shell grit brings the pH back into line (approx pH 7.0).

So I figured it might be a good idea to raise my seedlings in shellgrit.

I started with a food container, and drilled a few holes around the base.

Then added the mesh from a stainless steel sieve, and filled it with shell grit.

Shell grit can be bought where ever you might buy chicken feed, as they sell it to people who have chickens. Chickens eat it and it helps make their eggshells strong.

I chose a space close to the water inlet in the growbed to bury it so the water flowing through would have high levels of dissolved oxygen. I figured this might be important as the flow through the tightly packed shell grit would be slow.

I buried it at a depth so the water level just reached the shell grit. The water "wicks" up through the shell grit so it stays moist.

I also added a lid in the form of another food container.

I'm not sure if the lid is needed, but a lot of store bought seed raising trays have lids so I thought I'd add one. It probably isn't required because I'd guess the lids are used to keep the moisture in, but with water always wicking up from the bottom...

Who knows.

I have no idea if this will work, but as always, I'll let you know one way or the other.

120 Things in 20 years - My ribs hurt.

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