Most large scale aquaponics systems use a filter system setup that includes a centrifugal ‘solids filter’ which settles the actual fish poo solids out of the water so that it never reaches the grow beds. A media filled grow bed WILL filter out the solids for you. About the last thing you want is solids settling in your grow bed, as this will accumulate into a stinking mess! Not good for your in home aquarium.

There are a couple ways of making a ‘solids’ pre filter for your grow bed if you aren’t using an external canister filter.

If you are using a power-head for an undergravel filter you should be already set up with a solids pre-filter. The aquarium gravel will work quite well for this task. You just need to siphon clean the gravel at the normal regular intervals. There may be a few instances where you could have solids pass through the gravel though. If your power head is too powerful for the size of under gravel filter you have, or if the gravel isn’t deep enough to adequately capture the solids - either there is a hole or thin spot, or you don’t have enough.

Adapting an existing filter

If you are using a regular submersible water pump or you feel that your canister or powerhead pumps don’t do a good enough job, you can build a pre-filter right at the grow bed.

If you have an extra over-the-back hang on filter, you can pump water into that, and allow it to filter the water into your growbed. Even if the motor is burned out, makes an awful racket, or otherwise doesn’t work, it won’t matter as we aren’t using the motor .
You will likely need to leave the motor attached though, is they often time plug a hole on that side. If it leaks, take it off (usually a half twist of the pump motor) and add a little petroleum jelly to the rubber o-ring, or if it’s really bad, replace the o ring, and then reinstall the pump motor.
Take the pickup tube that came with the filter off, as we don’t need this. Let the water pour into the filter either in the area where the pickup tube used to be or behind the media.
You can use regular filter refill kits doing it this way. When the filter media gets filled up, it will then overflow onto the pickup tube side. Clean or replace the filter media at this point. I usually get several cleanings before I need to replace the media. Make sure you use cold or luke warm water to clean it as hot water will kill the beneficial bacteria in the filter. Never use soap.

Building a filter housing from scratch

If you want, you can also build a solids filter from a plastic container. I would first see what’s readily available for filter media and inexpensive in your area. If you can get the best price on round cut foam for canister filters, then round containers such as juice pitchers would be the container of choice. If it’s square or cut to fit, then a rectangular container may be better. Loose aggregate type materials will fit in either, obviously.

If your going to set the filter into the grow bed, then get either 2 containers that nest into each other or get a 2nd larger container that you can put your filter into. This will allow you leave the larger container in the grow bed while you clean the filter container and not worry about the grow media filling in the hole. You could also just set the filter on top of the media, but this may not look as good as having it half buried in the back. I also feel that having the filter buried will be less likely to have it tip over and have the pump hose fall out of the grow bed and pump all your aquarium water on the floor.

Try to get an opaque lid for the container. The pump outlet can create a lot of splashing so a lid would reduce the water loss and smell. Having no light pass through the lid will reduce any algae issues as the pre-filter is likely to be in a well lit area - directly under your grow lights.

Example top down flow filter

This example is for round filter foam and a container such as a juice pitcher. This style will only work if your foam filter pads are the same size or slightly larger then your container.



Theory of operation:
The water is pumped into the top of the filter container where it splashes out onto the aggregate. The water filters through the aggregate so that when it reaches the bottom of the pile, the water is evenly spread out and flowing evenly into the foam filter pads. The Foam filter pads filter out the solids. The water flows out holes in the bottom of the container into your growbed.

Instructional Video

Needed parts:

• Filter Container
• Larger Container (optional)
• Course aggregate
• Bioballs
• ceramic tubes
• course stone
• course crushed sea shells if these are part of your water chemistry treatment plan
• foam filters
• small support container (optional) (margarine container?)

Needed Tools:

• Drill
• Drill Bit

Instructions:
You will want to put everything together before you drill any holes so you know that it fits well.

If you have a lot of foam filter pads, you can start them at the bottom of your filter container and stack them up half way to the top. If you only have a few, you will want to first put the small support container in first, then stack up the filter foam pads on top.

The aggregate gets poured on top of the foam pads.

If everything fits well, you can take it apart and drill your holes. The aggregate should not want to fall down between the edges of the foam and the container. The system should be pretty full of medium, but not right up to the top. You will want a couple of inches above the aggregate for water to pool when the filter starts to get plugged up and the water flow slows.

Time to drill the holes.

If you are using the storage container, you will want to drill holes in the lid and the sides so water can flow through it. If you don’t have a lid, you can turn it upside down and have the holes in the bottom and sides. The idea is to support the foam, so the widest end should be up to provide the best support. Lots of holes is good. You just don’t want so many that the container is weakened and collapses when the foam and aggregate are added.
You then drill holes around the outside of the container. You will want to keep the main container holes below the top of the support so the water flows all the way through the foam filters. Several good sized holes are all that’s needed. Too many are better then too few.

If you are using foam pads all the way to the bottom, you will need more holes. A lot more holes. The idea is to have lots of ways for the water to flow through the foam so it’s less likely to plug up. You will want to drill holes up only one or two pads height from the bottom.

If you are using a juice container, you can likely feed the water hose through the pour spout. If not, either drill a hole in the side near the top or in the lid for the water hose. Try to get the hose situated so that it will direct the water near the center of the filter. You may want to drill a small hole so that you can zip-tie the hose in place. Hoses like to jump around when pumps first turn on such as when the power goes out and comes back on. It would be a bad thing to have the hose jump out of the filter.

If your truly paranoid (like me) you can drill an overflow hole near the top, but below the hose inlet. This can either be drilled so any water coming out goes towards the center of the grow bed instead of out, off the side and onto your living room floor or have an overflow hose that directs the water back into the aquarium.

Assemble your new filter, hook it up and see how it works. You should now have a grow bed that will stay cleaner for a much longer period of time. If the filter starts to smell or water starts accumulating at the top, it’s time to clean it. Rinse everything with cool water. Again, don’t use any soap, we have lots of good bacteria in this filter!