Backyard Aquaponics
A place to discuss aquaponics

I like the idea of having a variety of media as well. In my prototype system, I'm going to use the top of the IBC tank as another grow bed and likely will pipe the water from the sand bed (filtered) into the IBC bed (either gravel or expanded clay pellets) before sending it back into the fish tank. I'll update my graphic to show this since right now it shows the tank water being pumped directly into both the sand and IBC beds.

Here's an updated graphic that shows the filtered water from the sand bed returning to the fish tank as well as the secondary (IBC) grow bed. In this setup, I'll either have to raise the sand bed or lower the fish tank in order to get the returning water to flow into the second bed.

If you intend to run your dual system exactly as pictured, I would suggest you reread the iAVs instructions regarding the water. You only pump water for 15 - 20 minutes every 2 hours, not constantly as a raft system requires. IAVs could be described as a "Flood and Drain" system, although not the same F/D as in the gravel systems. If you intend to run your large iAVS on a constand flow as a filter for your small raft, that's your decision. It might work, but I don't think your iAVS will do very well. BUT, as you've probably seen, there's lots of different ideas/opinions about what will, does, can, might work with just as many different avenues to get there. If you want to do iAVs, I would suggest following the prescription for iAVs as described on the iAVs site until you're comfortable with what you're doing. If raft, FD, NFT, constant flow, etc is where you're heading, pick one and work with that. From what I've seen, it's rare to see two different systems melded together into one system with good results. I'm sure it's possible, but not necessarily for (no offence intended) beginners. If you want something simple to operate, it doesn't get much more simple than iAVs. Just my opinion.

Hi Aufin,

Thanks for your comments! Yes, I intend to run the sand bed as a flood and drain system. Hadn't thought about the impact of that on the bed above the tank. But it was to be a flood and drain system as well (just with different media).

Jeff

You should not try to use 2 pumps, they dont balance well with each other long term, even if you use the same model.

pumping to both or gravity feed from one to the other is the best way.


Your second media bed will be fine along side the sand bed, if you can only run every 2 hours with sand (why? root rot?) the rock media bed will likely handle that too, or you could run the IBC bed as constant flood and the sand bed as flood and drain.

Hi Yavimaya,

Agreed on avoiding the two pumps! My aim is to create a simple, yet elegant system that is easy to run and maintain. My single pump will be in the fish tank in this prototype build.

The 2 hour interval for the sand, to my understanding, is to avoid over-watering (root rot) and likely has an impact on the bacterial environment. It makes sense to me that giving the bacteria more time to do their thing. I would guess (and that's all it is!) that there are different species of bacteria that function depending on how the moisture level in their environment. So more time between floods might be beneficial. From my hydroponic experience using flood and drain techniques, the other grow bed should be fine. I just don't expect it to do as well. But that will be a fun experiment.

im just not sure how hot it gets in costa rica and not sure that on your hottest day that a media bed will be so great with 2 hours of evaporation, but as constant flood it would be 100% fine.

it may be just fine like the sand bed, but bigger gaps in media make for quicker evap.

Good point. Fortunately, I am in the mountainous area of Costa Rica that stays amazingly temperate/spring-like year round. It's pretty humid too, especially this time of year (rainy season). With these conditions, it seems almost irresponsible not to do some aquaponics! :-)

I think if you want to set the system up as a true comparison to see what is going to be better you would need to do the two pump route, but one pump feeds the iAVs and the other pump feeds the gravel/hydroton above the fish tank. Then have them both drain back in to the fish tank, do not have the iAVS drain in to the gravel bed in that case otherwise it would be an unfair comparison because the iAVS is going to get all of the nutrients out of the water and you are going to provide the second bed with clean water... so two pumps would make sense in that case but they would be pumping to different beds and the drains would both go back to the fish tank.

the other thing to think about is if you plan to have pumps in the fish tank you have to keep the pump suspended so it doesn't accidentally drain the fish tank if something gets clogged, but in that case you aren't sucking the fish poo that settles on the bottom of the tank out. I don't know if that's the normal thought on IAVS or not? But to me it would still be beneficial to have a small covered sump sitting next to the fish tank that you overflow from the fish tank to the sump so you can put a SLO in, then pump from the sump to the growbeds.

Hi Rob,

Agreed about the comparison. This first prototype won't be about comparing systems though since I'm just trying to get a basic system going but at the same time, making use of the top of the IBC tank as a supplemental bed. When I do a comparison, it will be much more controlled, with same size grow beds, separate pumps, etc.

Good point re the pump in the tank. I was thinking to avoid the sump but I do like the SLO concept and it seems like a prudent move to avoid catastrophe! I could also use some kind of float valve/switch as well I guess. Maybe having a float switch to disconnect the pump power if the water reaches a certain level might be the easiest way to go. We are renting currently so am trying to avoid digging up too much of the ground!

Okay, so I'm thinking about the drain system for my iAVs bed. It's about a 1m wide by 3m long (at least it will be!). Aufin suggested that perhaps two or three smaller pipes running the length of the bottom of the bed might be better than a single 4" down the middle.

I think Gary or Mark mentioned that smaller than 3m you might not even need a central drain but I figure it might help draw the water down the bed a bit better. My system will also likely have a slight bow in the middle because I'm supporting the box with 2 rows of blocks. My thinking is that this might help with drainage as well.

Should I go with 2 or 3 smaller pipes running down the bed instead of the single middle one?

Comments? Thoughts?

The reason I'm using pipes is because I need to direct the draining water. Plus I didnt want my wood to stay constantly wet. Do some matth. Weight of your box filled with sand plus the weight of some water might be too much for your box. My 4 x 8 ft box has a ton of sand. The water draining is more important than a speedy drain. Don't try to overthink this. Pump your water in, let it drain out. Using the proper sand will take care of most of the drain issue. If you're concerned, a couple 2 inch drain outlets and a slight down tilt of the bed towards the drain. Of course, it's your project, so do what makes you happy.

You have been watching too many youtube videos.

water does not come back from beds nutrient free, sure the 2nd bed will get slightly less nutrients, but the nutrients build up in the water, it is not a "fish make nutrients, plants remove nutrients, clean water goes back to fish tank" like in all of "selling point" posters and videos.