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Didn't want to de-rail Grover's BBF thread so I will start a new topic about auto siphons.

There are at least three different designs and several variations of these auto siphons, but the principle is always the same.

* Water fills the tank which can take a while if the tank volume is large or the water flow is small.

* At the set volume (water height), the siphon self generates when internal air inside the siphon is displaced and the falling weight of water pulls more water down with it.

* A siphon drains water much faster than an overflow drain. If this is greater than the incoming water, the water level in the tank will drop until no more water is left to remove and air is sucked in which breaks the siphon cycle.

* A new cycle is completed and tank starts to gradually fill again.

Most commonly used in hydroponic flood beds.  Look up Bell siphon, affnan siphon, auto siphon etc. Youtube would have educational videos and clearer explanations so I won't bother but please ask if you have questions.

Onto the interesting usage aspect(s). Most fish keepers love water. I use auto siphons in a few different ways. These are not for everyone, but might be interesting for some and might spark some improvement ideas for others.

This is a simple auto siphon - hmm not sure if the photos will end up where I want them to be...

Siphon 01.JPG

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Usage #1 - Tank turn over

To keep the crap off the bottom of glass bottom tanks, most recommend a water flow which turns the tank volume over several times an hour. This stirs the muck into the water column and stops it from settling out so the power filter can pick it up.

For a 120 litre tank, it is pretty easy to turn over 3 times an hour but this becomes a bit more difficult for a 12,000 L tank or system of tanks. Yes it is possible with big powerful pumps but the running costs become prohibitive. A swim pool pump (high volume - high pressure) for example will do this effortlessly but power consumption is high. It is difficult to find high volume - low pressure water pumps unless you attempt to run several smaller pumps at the same time. Some pond pumps come close and more recent technology has improved this somewhat.

This is a photo of my goldfish racks. It holds 60 x 200L tanks (90cm x 60cm x 38cm) on three tiers. Goldfish are particularly messy fish.

The top tier of tanks each recieve a slow water fill from a central sump filter with the water pump. Every tank has air driven sponges, so the sump and water turn over is primarily for auto water change and evenly distribute water chemistry. However I want to reduce tank maintanance without high power bills.




With a corner divider in each tank, I create an internal chamber containing an auto siphon which will fill and fast drain. 



So top tanks slowly fill until this triggers the auto siphon drain which rapidly empties the corner internal chamber into the tank directly below to produce a quick fill (and stir) followed by a rapid drain into the tier below. If you look at the dark tank picture attached below you can see bottom pipes (45 degree elbowed pipes) which drop into the tanks below. I am able to use a 10,000 LPH pump to clean cost effectively.



The fish love the oxygenation aspects. And I fill the drain chamber with bio balls to make a wet dry flood zone of bio media because it would be a waste of energy not to.

This creates a noisy system so you do need to love the sound of water.


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Usage #2 - Rapid sump drainage

On another system I run 18 x 500L green tubs (9 tonne water). These are circular tubs so very easy to create a circular swirl flow with a tap positioned tangentially. With a central drain pipe and outer sleeve, I can pick up the bottom crap easily. In fact I can harvest fish by pulling both pipes and letting the fish drain out to a collection net in sump as the pipes increase in diameter. This system has automatic water change via a 24/7 constant drip.



One of the problems with this setup is the lack of space under the bottom tubs for a sump. I did not want to cut the concrete slab or put an external sump outside the shed (below ground). There is only 30cm clearance. It is possible to daisy chain several sumps to gain a bigger volume but that creates further issues. And I wanted a glass sump because I harvest fish through the sump. In fact, I empty one tub at a time during harvest by pulling out the central stand pipes drain.

So my sump needs to be big enough to handle the excess water (overflow from tanks) if a power outage occurs but this is very difficult on small sumps for large volume racks. However with the constant drip water change, the sump is quite full. This is also to safe guard against the pump running dry and burning out.



So I use an auto siphon on the sump which will rapidly drain water during a power outage. This still leaves enough water for the system to restart when the power returns and the drip will top back up within a day.



The U tube is the auto siphon. The adjacent vertical pipe (stand pipe drain) is the water height I want to retain in the sump. There isn't a lot of difference in height but these siphons can be very precise if you design with care. Take note of the siphon break hole on the U tube stem.

During normal use, the vertical stand pipe drains out the excess water from the constant drip. This does not need to be a big drain as even a slow continual drip can change considerable volumes of water. I set this for 20% daily as these are growout tubs.

During sudden water height increases, the vertical stand pipe drain can't cope so the water level rises until the auto siphon kicks in. This drops the water level down until the anti siphon hole is reached which breaks the sipon. And if water is still coming in and overwhelms the vertical standpipe drain again, the cycle repeats. This is quite reliable as there are no moving parts.


The photo below may explain better.

Ignore the downward elbow on closed valve tap as this is to drain the sump completely if I need to clean it. Having tight sump clearances create lots of issues.

I have started using sumps on steel post (rollers) to slide out now but that's another topic.





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Here is a photo of an auto siphon to create a flushing filter. This is an overhead filter using a 200L barrel but it could be in a sump and doesn't need to be as big.


The inside pipes before media is added - very simple. Water comes in through the 90mm pipe at top. The water level rises and falls inside the filter to create a wave tank.




The media used can be anything that doesn't float.

The photo below is rapid seeding of hydroton clay balls. No fish, just a heap of ammonia. If you want to boost other (hetrotrophic) microbes for bio film production you can add sugar as well. Power head circulating flow through an aged sponge filter.




This is the end result below. As I didn't want to waste the energy of pumped water up to the barrel, I decided to add a moving bed bedside the flushing barrel as well.

A moving bed of K1 is a bio film filter. Often confused with a fluidised bed filter. Happy to asnswer any questions but please google first as there is plenty of better explanations online elsewhere. Simplistically, having the media circulate to the surface allows fish waste and oxygen to the bacterial colonies. There is 16500 LPH of pumped water flowing through the moving bed barrel so the air pump is not necessary but it's a good safeguard against power failure if your air pump is backed up. This is energy wasteful so I was going to replace this with a normally closed solenoid tap to drain out. During a power outage the solenoid fails open so all the water drains out. However after some thought, I decided to drill a permanent 4mm hole. When the pump runs, there is plenty of water. If the power fails, the barrel will slowly drain allowing air to get in. No moving parts to fail. Saved $12 on a solenid tap. I have removed the air pump now.

After the moving bed, the water gravity drains into the flushing filter. The flushing filter will re-oxygenate the water and provide additonal bio and mechanical filtration. Instead of having the media move (like a moving bed filter) the water level rises and falls so oxygen and fish waste are brought to the media in a different way.


Flushing filter_resize.jpg


Photo of inside the moving bed filter below. The thinner pipe on right (40mm) is incoming pumped water which goes to the bottom of barrel and points back up to stir. The left thick pipe is 90mm stormwater as an overflow drain. It has lots of slits to stop K1 escaping and a T at top to let air out.


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I'm trying to imagine the aquarium this thing is attached to.  Must be some big monster tank!!

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21 hours ago, MFF said:

I'm trying to imagine the aquarium this thing is attached to.  Must be some big monster tank!!

Yes.. on a big tank. These blue barrels are the back up (redundancy) emergency filter as the main filter is outside the tank and much bigger.

However the same principles apply.



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