Couple of startup questions. Please help.

[Brooks Lindner]

My 13 yr. old son and I are starting a basic flood and drain system. Two questions: If our tank is 100 gallons, and our grow container follows the 1:1 ratio suggested in Bernstein's book, how much of the water do we "flood" the grow space with at a time? Too much and the fish don't have enough water. Too little and the plants don't have enough water, correct? Also, if we are doing system where the water drains back into fish tank using the same pipe that pumps water into grow space, won't the water pressure at the bottom of the fish tank prohibit full draining? Thank you for your help.

[Vlad Jovanovic]

Hi Brooks, many people will employ the use of a sump tank so that the fish tanks water wont fluctuate while fish tank water is filling the grow bed. 

If you have a 100 gallon container your'e using as a grow bed, after it's filled with media, expect it to hold a little less than half that volume. Generally most folks flood their beds to within 2" below the top of their media. Now, weather that's enough for the fish depends and how big you want them to get, type/quantity...

You might not "need" a sump tank, but it sure seems nice to have, especially if you want to expand and/or use the 2:1 ratio of grow bed to fish tank that many folks use.

As far as the plumbing question...IDK, I have not ever seen or heard of anyone ever arranging their plumbing in that way. Maybe someone else can help answer that. I'm not sure that I understand why you would want that sort of arrangement in the first place.

[Brooks Lindner]

Thanks for the quick response Vlad. I appreciate the feedback. The plumbing arrangement I mentioned is one of the examples in Bernstein's book. I suppose the reason for doing it that way is simplicity. But frankly it doesn't make sense to me with the water pressure issue. Any feedback from anyone else would be appreciated.

Vlad Jovanovic said:

Hi Brooks, many people will employ the use of a sump tank so that the fish tanks water wont fluctuate while fish tank water is filling the grow bed. 

If you have a 100 gallon container your'e using as a grow bed, after it's filled with media, expect it to hold a little less than half that volume. Generally most folks flood their beds to within 2" below the top of their media. Now, weather that's enough for the fish depends and how big you want them to get, type/quantity...

You might not "need" a sump tank, but it sure seems nice to have, especially if you want to expand and/or use the 2:1 ratio of grow bed to fish tank that many folks use.

As far as the plumbing question...IDK, I have not ever seen or heard of anyone ever arranging their plumbing in that way. Maybe someone else can help answer that. I'm not sure that I understand why you would want that sort of arrangement in the first place.

[Jon Parr]

As to the plumbing question, No. Water pressure in the bottom tank will not stop the backflow of water from a higher level. Think of a stray in your soda. When you you draw water up with suction (same thing as push from the bottom with pressure), the soda goes up the straw. When suction is discontinued, the soda drains back down until the level inside the straw is the same as outside the straw. Water always seeks it's own level, accross all connected bodies, always.

Using the pump line to drain the growbed is a bad idea, though. It works great in hydroponics, because hydroponics is clean and sterile, so the water goes up, and water comes back down. To some extent, the drain water even flushes the pump itself. However, with Aquaponics, we have living bacteria that thrives and forms bioslime. This slime will coat the pump, the tubing, the growbed and tanks, and will adhere to dust and grit, fish poo, roots, etc, and grow in size. When the pump kick on, it will accumulate slime in the bed near the inlet. When the pump turns off, this wad of slime plugs the drain tube, slowing the drain and accelerating the growth if the slime ball. Better off to top-fill a bed, so slims never goes back into plumbing.

[Brooks Lindner]

Thank you Jon. Could you please expand on the top-fill method?

Jon Parr said:

As to the plumbing question, No. Water pressure in the bottom tank will not stop the backflow of water from a higher level. Think of a stray in your soda. When you you draw water up with suction (same thing as push from the bottom with pressure), the soda goes up the straw. When suction is discontinued, the soda drains back down until the level inside the straw is the same as outside the straw. Water always seeks it's own level, accross all connected bodies, always.

Using the pump line to drain the growbed is a bad idea, though. It works great in hydroponics, because hydroponics is clean and sterile, so the water goes up, and water comes back down. To some extent, the drain water even flushes the pump itself. However, with Aquaponics, we have living bacteria that thrives and forms bioslime. This slime will coat the pump, the tubing, the growbed and tanks, and will adhere to dust and grit, fish poo, roots, etc, and grow in size. When the pump kick on, it will accumulate slime in the bed near the inlet. When the pump turns off, this wad of slime plugs the drain tube, slowing the drain and accelerating the growth if the slime ball. Better off to top-fill a bed, so slims never goes back into plumbing.

[Brooks Lindner]

Never mind. I know what the top fill method is. Thanks for the feedback.
Jon Parr said:

As to the plumbing question, No. Water pressure in the bottom tank will not stop the backflow of water from a higher level. Think of a stray in your soda. When you you draw water up with suction (same thing as push from the bottom with pressure), the soda goes up the straw. When suction is discontinued, the soda drains back down until the level inside the straw is the same as outside the straw. Water always seeks it's own level, accross all connected bodies, always.

Using the pump line to drain the growbed is a bad idea, though. It works great in hydroponics, because hydroponics is clean and sterile, so the water goes up, and water comes back down. To some extent, the drain water even flushes the pump itself. However, with Aquaponics, we have living bacteria that thrives and forms bioslime. This slime will coat the pump, the tubing, the growbed and tanks, and will adhere to dust and grit, fish poo, roots, etc, and grow in size. When the pump kick on, it will accumulate slime in the bed near the inlet. When the pump turns off, this wad of slime plugs the drain tube, slowing the drain and accelerating the growth if the slime ball. Better off to top-fill a bed, so slims never goes back into plumbing.

[TCLynx]

I've done the "ebb and flow" (where you pump up into the bottom of the container and then it drains back down through the pump line) in a few trays I've used attached to the aquaponics.  It can work though I wouldn't do it without the understanding that extra cleaning may be needed.

I prefer the timed flood and drain where you pump up above the grow bed and let the water drain down into the media and then in another location you have a standpipe drain.  The stand pipe has a couple holes near the bottom to let the bed drain slowly when the pump turns off and the top of the stand pipe is set to regulate the max flood level so the top of the media stays dry, usually between 1-2 inches below the top of the media.  Make sure that stand pipe is removable/accessible for cleaning, use a gravel guard around all drains to make this possible and keep you rmedia out of your drains or siphons.

[Sylvia Bernstein]

Hi All.  Coming from a hydroponic background the "ebb and flow" method of draining back through the pump is what came naturally to me so that is how my first non-sump designs were configured...and those systems have been running just fine for the past few years.  You do, however, end up with more of an accumulation of solids near the inlet / outlet (same thing since everything goes through the pump) than I would imagine you would if the water entered the bed in another location.  My worry with that design has always been that those small holes at the base of the stand pipe would easily get clogged.  Our Designer system uses that approach, but instead of having the small holes the tubing running out of the base of the bed has a valve on it.  This has worked well because it is adjustable, vs. holes that aren't.

[RupertofOZ]

The hydroponics "ebb & flow" style ... back draining through the pump... is the most common design used by those with previous hydroponics experience... and particularly by hydroponic shops and suppliers as they climb aboard the aquaponics train... wihout perhaps having investigated, or understood the principles of flood & drain as it's applied in aquaponics...

 

As Sylvia says... it results in an acculmulation of solids near the inlet/outlet.... and during the timer off cycle... within, and/or around the pump itself...

 

The drain back through the pump also tends to macerate any solids.... this is not good for either the pump... or for an aquaponics system... as it results in high levels of suspended solids in the fish tank.... and possible anaerobic processes developing either within the beds, or within the pump... during the "off" cycle.... however short, or sporadic that off cycle may be...

Raising the level of suspended solids in the water.. also raises the BOD... biological oxygen demand...basically robbing the system of oxygen...

 

And the "ebb & flow" style negates, or significantly reduces the benefits of oxygenation acheived through "flood & drain" water return from the beds...

 

It can also result in the accumulation of any worms in the beds... often totally overlooked by the hydro implementations... near the inlet/outlet... and result in them being sucked down through the pump into the fish tank...

 

There really is just no benefit in employing "ebb & flow" in an aquaponics system... and IMO... it should be totally avoided..

 

Sylvia, I'm not sure what you mean when you say you're worried about the "holes in the base of the standpipe would easily get clogged".... in a top filled timed flood & drain... this is just not an issue...

 

The only time the drain holes might become clogged... is due to root growth through the media guard...

 

Not sure either Sylvia, by what you mean by "instead of having the small holes the tubing running out of the base of the bed has a valve on it.  This has worked well because it is adjustable, vs. holes that aren't".... can you post a diagram, or photo... I don't grasp what it is that you've done...

[Brooks Lindner]

Awesome replies one and all. Very helpful. I appreciate it.
RupertofOZ said:

The hydroponics "ebb & flow" style ... back draining through the pump... is the most common design used by those with previous hydroponics experience... and particularly by hydroponic shops and suppliers as they climb aboard the aquaponics train... wihout perhaps having investigated, or understood the principles of flood & drain as it's applied in aquaponics...

 

As Sylvia says... it results in an acculmulation of solids near the inlet/outlet.... and during the timer off cycle... within, and/or around the pump itself...

 

The drain back through the pump also tends to macerate any solids.... this is not good for either the pump... or for an aquaponics system... as it results in high levels of suspended solids in the fish tank.... and possible anaerobic processes developing either within the beds, or within the pump... during the "off" cycle.... however short, or sporadic that off cycle may be...

Raising the level of suspended solids in the water.. also raises the BOD... biological oxygen demand...basically robbing the system of oxygen...

 

And the "ebb & flow" style negates, or significantly reduces the benefits of oxygenation acheived through "flood & drain" water return from the beds...

 

It can also result in the accumulation of any worms in the beds... often totally overlooked by the hydro implementations... near the inlet/outlet... and result in them being sucked down through the pump into the fish tank...

 

There really is just no benefit in employing "ebb & flow" in an aquaponics system... and IMO... it should be totally avoided..

 

Sylvia, I'm not sure what you mean when you say you're worried about the "holes in the base of the standpipe would easily get clogged".... in a top filled timed flood & drain... this is just not an issue...

 

The only time the drain holes might become clogged... is due to root growth through the media guard...

 

Not sure either Sylvia, by what you mean by "instead of having the small holes the tubing running out of the base of the bed has a valve on it.  This has worked well because it is adjustable, vs. holes that aren't".... can you post a diagram, or photo... I don't grasp what it is that you've done...

[Sylvia Bernstein]

Instead of relying on small holes in the stand pipe which, as you pointed out, can become clogged with roots and other matter, we have put a second bulkhead in next to the stand pipe to drain the bed, and a valve on the exiting tubing so we can adjust the rate at which the bed drains.

[TCLynx]

So Sylvia, it's a stand pipe Overflow and next to it a drain controlled by a valve?  Is that right?

Otherwise I was going to worry that without an overflow, if the valve gets blocked it could be major HSM.

[RupertofOZ]

A pic would be helpful...