Aquaponics - Venturi

A venturi is a lot of things, but in an aquaponics system it's a noun, and refers to a way to introduce lots of air bubbles into a stream of water.

It tuns out, if you have an elbow in a pipe, or some other temporary restriction, the water is under increased pressure before the restriction, and at a lower pressure immediately after the restriction.

The odd thing about that, is that its useful.

Who would have thought.


If you have a restriction in a pipe and you prick a hole just before restriction (between the pump and the restriction) you get a leak in your pipe. We hate leaks, so don't do it.

But if you prick a hole in the pipe just after the restriction (between the restriction and the fish tank) you get a venturi. Actually you probably get something called a venturi effect air tube or something.

But what you really get a venturi.

As the water gets near the restriction, it slows down and as result, there is a pressure localised pressure increase. When it passes through the restriction and opens back up to the normal pipe size, it is allowed to speed back up, and as a result finds it self at lower pressure.

I think.

If there is a hole in the pipe where the pipe is at higher pressure, the water looks to escape, and does so through the hole. If there is a hole in the pipe where there is a lower pressure, the water is quite content to be in the tube, because like everyone else, if your situation is getting slightly easer to move around, and you are under slightly less pressure than you were a while ago, you become content.

The result of a low pressure area with content water is that it sucks in air instead of spitting out water.

This can be a good thing if you are trying to put air into your water, or break up the surface tension on the top of your fish tank, or trying to make one of those low flow shower heads that don't quite wet you as well as just dumping a stack of water on your head.


But dont take my word for it.

I'll build one.

I have a pipe flowing water into my new IBC fish tank.

Try not to notice the massive algal bloom that's occurred as a result of there being too much nutrient in Adelaide water, and the tank just sitting for a week or so.

That's water, not a sports drink.

When you submerge the end, it looks like this.

Interesting, isn't it.

Next we prick a small hole in the tube about halfway along its length.

I was looking for something like a nail to prick a hole in my hose, and found this instead.

I just worked out what it's for. I've had it for ages.

One end has a point for putting holes in black poly pipe, and the other end has a hex spanner for  screwing in the little connectors that have a point on them for things like dripper systems, and little sprinklers etc.

So far in my life, on the odd occasion when I've done such gardening stuff, I've been just forcing the connector things through after making a hole with a nail.

This tool thing works really well.

Anyway...

I turned off the water flow and made a hole.

Interestingly (this isn't the interesting bit) the water dribbled out a bit...












and... (<= that's the interesting bit)

also made a few bubbles exit the pipe under water.

When I created a restriction in the pipe below the hole we see increased pressure as the water piles up at the restriction, and distinctly more water exited through the hole. The photo didn't really capture it, but it was probably 5 times more water.

We also see no air exiting the tube at all.

But when I create the restriction before the hole, we see no water flow out of the hole at all.

And a stack of bubbles exiting the pipe under water.












There, except for any errors I've made, that's probably all you will ever need to know about a venturi.





This 120 Things in 20 years post, looked like something on the venturi effect in an aquaponics environment, but I think in the future's history, it will prove prove to be part of something more to do with the Murray river and the environment.

Aquaponics - Water testing

Its extremely important to make sure your water quality is within a desirable range. Aquaponics is remarkably stable and robust, but, for the first few weeks of setting up a new system it can require a little extra care. The best way to avoid any problems is to test your water every day until your system is mature and in balance or "cycled". (pictured here taking 30 days or so)

An aquaponics system is said to be cycled when it can process approximately 1 ppm of ammonia into nitrites and then process those nitrites into nitrates within 24 hours.

A decent freshwater test kit will enable you to get accurate test results for pH, ammonia, nitrites, and nitrates. It will set you back around 50 Australian dollars. They are widely available online or any good aquarium shop should sell them.

If you try aquaponics without water testing you will lose fish unless you are very lucky.

Add ammonia until you see a reading of 2ppm, then wait until your tests show ammonia is 0. Then add more and continue until your system can process 1ppm of ammonia and nitrites in 24 hours. Once you see readings of 0 ammonia and 0 nitrites you are cycled and can add fish.

Plants can be added on the day you first build your system but there wont be much for them to live on for a few days. My house water supply is rainwater and has some nitrates in it from normal environmental nutrient. Even normal tap water will have some nitrates in it so there will actually be something for small seedlings to live on.

Be careful to wash the soil from any store bought seedlings you transplant as they may have any number of additives that may be toxic to an aquaponics system. Growing directly in the grow beds from seeds is safest (and often quicker!)

Conduct water testing every day until you are cycled and then test every week or so or if ever anything strange occurs. Plants yellowing or dying can be a sign of something being wrong with your water chemistry and you might need to intervene in the early stages of your aquaponics system setup. More on correcting water problems later.

Always keep a record of your tests so that you can see emerging trends before they become an issue.