Fish Filtration

[David Nabong]

Okay, so this probably belongs somewhere else but I can't decide where. 

 Besides the grow beds are anybody  using filtration for the fish tanks?  I understand for NFT & Rafts most are doing some sort of mechanical or settling filter, although I haven't seen the reasoning completely defended.  Being a fishkeeper wanting to convert, I'm having a hard time letting go of filtration for the fish themselves.

Since I want my tilapia to grow to a breeding population, I want to have sponge filters for the fry, and right now since I have 2:1 water to fish ratio in one of my tanks (fingerlings only) my filter rate is in the range of 3x volume of tank per hour.  For my "ornamental" tank I'm in the range of 6X per hour, so I'm having difficulty reckoning with having my veggies do all that work.

Don't get me wrong, I'd love to get rid of my energy consuming canister filters, but what about the fish, we are going to eat them after all.

[TCLynx]

Good Question.

Now media filled grow beds do provide a huge amount of filtration and one could (proving the fry don't get sucked into the pump) skip the canister filters if you have enough media based filtration to support your fish load and you move enough of your tank water to keep the water quality up to your standards.

But you are right in thinking something may be missing if you were just to simply hook a heavily stocked fish tank to a NFT pipe with no filtration and call it aquaponics. (The times I've gotten questions from people who have tried this because some one told them that aquaponics was simply hydroponics crossed with fish, the people were struggling with problems of fish poo building up and going anaerobic in the NFT troughs.) And a similar issue can arise with a heavily stocked fish tank flowing unfiltered into a DWC raft bed.

The trick is there is definitely bio-filtration provided by all surfaces in a system, however, you have to make sure there is plenty of dissolved oxygen in the water to go around and that it doesn't become depleted at some point in the flow. Excess solids building up somewhere in the system can cause this.

Anyway, there are some very low stocking density systems out there that are simply fish tank flowing to raft tank with a little pumping and supplemental aeration and that is it but again those are very low density systems and really so far only tested with tilapia as far as I know.

Most systems using rafts or NFT pipes have some additional filtration. Some have combo systems with gravel beds feeding rafts or NFT pipes since the gravel beds provide great filtration. Other systems have swirl filters or clarifiers and then bio filters or mineralization tanks or net tanks before the water flows into the raft beds.

However, if you are planning to use the aquariums that are already in place, you could simply continue using the current filtration if you wished and just send the filtered water through your preference of plant growing method before letting it return to the fish.

[David Nabong]

So, "potentially" the grow bed could be sufficient as mechanical and biological filtration, however several of the threads here debate the proper media bed to fish load ratio. Also, I have found that there is no clear consensus on what are the best flood drain intervals, and it seems that there is a fairly even split between siphon and timer drain cycles.
Also, one of the topics that doesn't seem to be touched upon is the use of air lift to grow beds. I haven't tried it yet, but I think that it is probably too slow a flow rate to start the siphon cycle. I'd like to think it could work though.
I see that you have several different systems working currently, which is working best for you? Are you using different systems for different plants, etc, etc.?

TCLynx said:

Good Question.

Now media filled grow beds do provide a huge amount of filtration and one could (proving the fry don't get sucked into the pump) skip the canister filters if you have enough media based filtration to support your fish load and you move enough of your tank water to keep the water quality up to your standards.

But you are right in thinking something may be missing if you were just to simply hook a heavily stocked fish tank to a NFT pipe with no filtration and call it aquaponics. (The times I've gotten questions from people who have tried this because some one told them that aquaponics was simply hydroponics crossed with fish, the people were struggling with problems of fish poo building up and going anaerobic in the NFT troughs.) And a similar issue can arise with a heavily stocked fish tank flowing unfiltered into a DWC raft bed.

The trick is there is definitely bio-filtration provided by all surfaces in a system, however, you have to make sure there is plenty of dissolved oxygen in the water to go around and that it doesn't become depleted at some point in the flow. Excess solids building up somewhere in the system can cause this.

Anyway, there are some very low stocking density systems out there that are simply fish tank flowing to raft tank with a little pumping and supplemental aeration and that is it but again those are very low density systems and really so far only tested with tilapia as far as I know.

Most systems using rafts or NFT pipes have some additional filtration. Some have combo systems with gravel beds feeding rafts or NFT pipes since the gravel beds provide great filtration. Other systems have swirl filters or clarifiers and then bio filters or mineralization tanks or net tanks before the water flows into the raft beds.

However, if you are planning to use the aquariums that are already in place, you could simply continue using the current filtration if you wished and just send the filtered water through your preference of plant growing method before letting it return to the fish.

[TCLynx]

I'm using many methods and what is best will depend on many factors and the particular situation it is in. Flow rates or pumping cycles/drain intervals etc really depend on the need for filtration and aeration for the fish, as long as the water is well aerated and flowing, I've found the plants don't seem to care too much what exactly the interval is as long as they don't dry out.

Airlift pumps they have pros and cons. They definitely are not meant to lift water very high and their efficiency is definitely questionable if lifting water is all you are trying to do with the air pump. Only real benefit I see to them would be that one might use a large blower to operate aeration and airlift pumping for multiple systems in a larger operation and avoid the separate water pumps and need to have electricity close to the water. If you are talking about a small system with no larger air pump/blower on site, or a situation where water is being lifted more than a few inches, water pumps will probably be more efficient at moving water.

I'm primarily a media based grower though I do have a couple runs of NFT pipes and I'm starting to experiment with a raft bed. So far the media is of course the best and I wouldn't do a system without at least some media bed. However, each type has it's purpose. The basil and lettuce grow great in NFT. I still can't say what I think of rafts yet.