Filter for DWC

[Craig Hartsough]

Hi everyone, I am wondering about they type/extent of filtration needed for a DWC/ floating raft system. I've a 1,000 gallon of fish tank so my flow rate will have to be about 12GMP I believe. My goal is to avoid synthetic media filtration. I have a 240 gallon conical tank that I am installing a series of baffles into so the water will slow and the large particles will drop out. Some people say this is all the filtration I will need, others say I need to invest in an aquaculture beed filter which will run me around $500. What if I have a 4'x2'x1' gravel filter after my solids collector, would this be sufficient? I would appreciate any comments or ideas. Thanks!

Craig Hartsough

Creekside Aquaponics

[TCLynx]

I'm not sure if that size gravel filter will be sufficient for your system but I do know that gravel beds can function as all the filtration needed for a system.  My systems have no solids settling tanks and they simply flow through gravel beds for all my filtration, I really don't use DWC much on my systems.  I am able to pump water from my gravel bed filtered sump water right into NFT pipes and the water is clean enough for that.

 

So, if you are removing solids with your settling tank and just catching the fine stuff in the gravel bed, you will just need to judge if that size gravel bed is enough for the load you put on it (that will depend on fish stocking and feeding rates and the frequency that you remove the solids from your settling tank.)  It will probably be a wait and see if your gravel bed starts to clog or not.

 

For pure flood and drain media bed systems, it generally takes somewhere between equal volume of gravel to fish tank up to twice as much gravel as fish tank and large enough gravel along with composting worms to keep the gravel from having clogging issues depending on fish load.  But that is without any sort of solids removal before the grow beds.

 

[Ryan Chatterson]

Bead filters are pressurized anyways so I'm not sure how you would do that after the conical clarifier. I say not needed, just build a longer tank after the clarifier and fill it with something like shade cloth or any other material you can think of that's fish safe to knock the suspended solids out of the water. That clarifier is only going to remove 50-60% of the solids so IMO, you need something afterwards.

TCLynx said:

I'm not sure if that size gravel filter will be sufficient for your system but I do know that gravel beds can function as all the filtration needed for a system.  My systems have no solids settling tanks and they simply flow through gravel beds for all my filtration, I really don't use DWC much on my systems.  I am able to pump water from my gravel bed filtered sump water right into NFT pipes and the water is clean enough for that.

 

So, if you are removing solids with your settling tank and just catching the fine stuff in the gravel bed, you will just need to judge if that size gravel bed is enough for the load you put on it (that will depend on fish stocking and feeding rates and the frequency that you remove the solids from your settling tank.)  It will probably be a wait and see if your gravel bed starts to clog or not.

 

For pure flood and drain media bed systems, it generally takes somewhere between equal volume of gravel to fish tank up to twice as much gravel as fish tank and large enough gravel along with composting worms to keep the gravel from having clogging issues depending on fish load.  But that is without any sort of solids removal before the grow beds.

 

[Craig Hartsough]

I am burying my fish tanks so they will be the lowest point in the system, that way I eliminate the need for a sump and the tanks will be very well insulated. My solids collector/clarifier is the highest point in my system. I am interested in DWC for its commercial applications and I am avoiding the gravel ebb and flow system for this project. Just out of curiosity TCLynx, what is the volume of your gravel filtered sump and what is the volume of your fish tanks? Just so I have a general idea of the ratio that you have been successful with. Thanks for the tips Ryan, perhaps I can use shade cloth or something similar and put that directly in the last compartment of my solids collector/clarifier. Otherwise, I will add an additional tank after the clarifier and use gravel or shade cloth or some other medium to filter the smaller particles the clarifier missed. VERY helpfull guys thanks! This forum is awesome!

[TCLynx]

My big system has a 700 gallon fish tank and about 1400 gallons worth of gravel beds (I do sequence the flow a bunch of the beds using Aquaponics Indexing Valves.)  My "clean water sump" that feeds towers and NFT pipes as well as back to the fish tank is only about 300 gallons.  My Big system is essentially a CHIFT PIST system though it has gotten more complex than that.

 

Having a fish tank flow into a clairifier (solids settling) tank then have that flow into a net tank then into the degassing tank before feeding the rafts then pumping back up to the fish tank works well.  However if your fish tank is the lowest position and you are having to pump (read blend) the solids to the clairifier tank, you will have far more solids staying suspended since they will have been blended up and more mineralization tank net tank or gravel bed will be needed to catch the solids unless you are going ultra low density on the fish side.