Aeration And Water Movement

 

These plants thrive right above the air stone!  (LINK)

Could this be caused by the movement of water through the roots or is it increased oxygen?  In any case, whether it's due to increased oxygen or water movement it is obvious that air stones in the raft tank are quite beneficial.

I asked Forest, my friend and hydroponic guru, if it might be due to water movement.  He felt strongly that it's the improved oxygen in the water rather than water movement.  I'm still on the fence about that, but Forest really knows about hydroponics so I tend to believe what he says.

But this has gotten me thinking  about adding an aquarium PowerHead and/or incorporating an Under-Gravel Jet System as described at this link.  The Under Gravel Jet appears to be very similar to a Fluidized Sand Filter.  

I found this article about designing a Fluidized Sand Filter.  

Further research shows that they can be designed to remove Nitrates as well as Ammonia and Nitrites.  This of course is not what we would desire in an aquaponic system, but it appears easy enough to avoid removal of Nitrates by not building the filter too deep.

 


Devin uses very large 12" air stones in his raft tanks under the gravel.  Yes he places gravel in the bottom of his Floating Raft tanks.   His results are astounding and I tend to agree with Devin about Rafts vs Gravel beds.   Transplants do better when placed into a raft and growth rates seem to be better, and with good aeration the raft systems can only be improved.

I bought a Hydrofarm Active Air Pump.  
It's a bit noisy but an optional volume control can turn adjust the volume and the noise.

* UPDATE October 10, 2012 -  This Hydrofarm pump has been running 24/7 for 4-1/2 months.  It progressively became louder until it sounded like a jack hammer.  Two days ago I turned it off and replaced it with a new EcoPlus Commercial Air 5.   Even after rebuilding it with parts supplied by the distributor it was no longer working properly.    I have high hopes for the new EcoPlus Commercial Air 5.  It runs much cooler than the Hydrofarm pump which ran so hot I could not even touch .
The new EcoPlus Commercial Air 5. is by no means silent, but it purrs with a low tone rather than a raspy and unpleasant noise. 

The noise was too much so I placed the air pump inside my shop and plumbed the line out to the system

Here's a video about how to repair an air pump

Today I placed four fat air stones in this raft tank under about 4 inches of gravel.

 

It's about time to make some better rafts 8-)