How long till it clogs

[Jeremiah Robinson]

I'm trying to figure out how to quantify and estimate the media cleaning schedule for an all-in-one flood-drain media bed system.

It seems like your cleaning schedule would depend on the following factors:

• Fish feed rate
• Media size
• Grow bed horizontal surface area
• Grow bed depth
• Uniformity of solids application
• Solids removal (if applicable)

Dr. Lennard in his calculator recommends every 3-6 months, which is a shorter maintenance cycle than I've heard of others using on this forum and elsewhere.

Does anyone know how to quantify this, or have practical/anecdotal experiences as to how often you have to clean your media?

[Jeff S]

Oh the tapered GB was just a thought. I already have an IBC setup that I'm expanding right now. I started with 5 Tilapia and it didn't take long to grow that # to over 800. That's been my problem. I haven't been able to grow the fish because of ammonia build up. Had to cut back on feed. Just couldn't bring myself to flush any fish. So I take it from what you're saying is I can densely stock when I add a larger RFF and a couple more beds. Do you use additional filtration?

[Vlad Jovanovic]

You may also want to consider adding to your list of factors 'plant cultivar'. If all other things were equal...there's a quite a difference in a grow bed that is consistently and exclusively planted with lettuce and spinach, as opposed to one stocked with tomatoes and cucumbers (because of the vast differences in root mass).

[Jeremiah Robinson]

I was trying to emphasize the fact that the media beds can handle a crap load of fish waist, so long as they are built deep enough with the right size media and worms.

Can you define a crap load :)  

I also really like the spelling of "fish waist" :)

[George]

It's a two inch layer because of the design - there's a drain hole in the standpipe approximately two inches from the bottom of the bed, just about an elbow of two-inch pipe.  It gets flushed somewhat but still holds water and solids after the drain cycle.  Anaerobic?  Possibly but I don't know.  There are certainly some solids captured at the bottom of the beds and throughout the media but they don't seem to cause problems.

Jeremiah Robinson said:

That's interesting.  I would guess that that 2" layer is anaerobic, unless worm castings have some kind of special consistency that anaerobic bacteria can't live off them.  Or perhaps the worms eat that bacteria.  

Do you have any idea if that layer has grown over time?  If it's 2" after 3 years, it would presumably be 4" after 6 years.  In 24" beds that may not be a problem.  In 12" beds it seems like it might be.

[George]

Throw a largemouth bass in the tank and he'll help you reduce the tilapia.  You can eat him later.

Jeff S said:

 I started with 5 Tilapia and it didn't take long to grow that # to over 800. That's been my problem. I haven't been able to grow the fish because of ammonia build up. Had to cut back on feed. Just couldn't bring myself to flush any fish.