Constant Flow versus Flood & Drain

[winger4647]

I have read through some of the literature on this forum on both of these types of water supply. From what I have read the F&D is better than the constant flow floating beds according to Oliver. He does not specifically say how the floating beds were fabricated. I am going to make some assumptions here.

1) the F&D allows the roots to access oxygen when there is no water
2) the CF has a floating bed with the roots of the plant dangling in the water supply. Systems I have seen in pictures show the bed above with the water supply underneath sort of in an enclosed space. If the roots are entirely (or mostly) covered in water the only oxygen they will get is from the water and not the air. Even if they are not covered with water the gaseous oxygen in this enclosed space would or could deplete to some extent causing a deficiency?

If the floating bed was raised to allow air circulation or the floating bed was fashioned so only a portion of the root stock was touching water and the air space below the floating bed was open to atmosphere (not a sealed bed on top) would this not work just as good as the F&D?

Without doing any calculations it would seem to me that energy wise it would be easier and less expensive (pumps & energy) if there was a slow controlled flow over a flood type of system, especially if the tanks being used were somewhat on the same level with each other.

[Oliver]

Inasmuch as you mentioned my name, I assume you were referring to something I said in AP 101. AP 101 is about media filled grow beds only. Regarding them, it is better to flood and drain in order to purge the bed of most of its water. This operation allows for the near even distribution of the new water coming in. In continuous flow media beds the water forms channels where some portions of the bed do not receive fresh water.

This is all in addition to the aeration of the media and plant roots that contain the autotrophic bacteria living on their surface. The air doesn't directly come in contact with the bacteria but penetrates the film of water remaining after a drain. This water then passes the oxygen in the absorbed air to the bacteria and the roots of the plants.

If the water flowing into the deep media grow bed contains high levels of oxygen, then the aeration of the film is less important as it is already nearly saturated with oxygen.

In either case, the bacteria and plant roots require a flood and drain operation to replenish the bacteria and plant roots with fresh nutrients.

Also, the amount of energy is roughly the same, regardless if you continuously flow water into the bed and allow the siphon to set the cycle timing or if you intermittently flow the water into the bed by some timing mechanism. On my personal single fish tank and multiple grow bed systems I started out with continuous input flow adjustment and let the siphons do the timing for the reasons of minimal parts count and cost.

I have since gone to timed valves so I could test out its feasibility. The advantage of timed valves is that the fish tank level is nearly always constant and the lines to the grow beds get purged every cycle with lots of water flowing through them for a short period of time.

The disadvantage is that the cost of the electric valves and electronics involved was quite high.

Oliver

p.s. You have posted this twice. I suggest you delete the first post.

[winger4647]

p.s. You have posted this twice. I suggest you delete the first post.

It was posted one time and it was listed one time earlier today. Why it is posted twice is beyond me! I did though remove it!

[JCO]

Is it Lettuce or $$$$$$ Check out the video here. It is a raft system and as much as I respect Oliver, I use a constant flow system all the time, sometimes with a raft (4' X 8' X 2" blue Styrofoam from Lowe's) floating on top and sometimes without as can be seen in the thread NOW YOU'VE GOT DUCKWEED...! and all its' posts.

It's all in learning how to do it and picking the way you want to operate. I don't have to clean out my grow beds which is a problem with media grow beds.

Media grow beds are unique to Aquaponics whereas in Hydroponics, you rarely see any such animal. They operate almost exculsively with constant flow sysems (rafts and NFT).

Media is basically a way to anchor the plants which can be done in other manners.

[Oliver]

There is no conflict here, as we are removing all of our media beds and replacing them with DWC and NFT.

In order to do that, we have to incorporate an advanced filtration system, as the fish solid waste must be removed from the water going into these growing mechanisms. The main difference is that we intend to keep the solids in the system by mineralizing them and using the extra nutrients they produce to grow more plants. We believe from the data we have, we can grow twice as many plants by doing this than we could if we removed the solids from the system entirely.

The only question that remains, is if we can grow tomatoes and other flowering plants in DWC. If not, we will have to incorporate some media grow beds.

And now you know what we are up to.

Oliver

[JCO]

Ah Ha...now that I have pried the information from you, I will tell the world what you have done...there is nowhere for you to hide

[dead_sled]

The main difference is that we intend to keep the solids in the system by mineralizing them and using the extra nutrients they produce to grow more plants.
Oliver

Interesting idea. Make use of it rather than throwing it out. Makes sense.

[rocketboy]

The main difference is that we intend to keep the solids in the system by mineralizing them and using the extra nutrients they produce to grow more plants.
Oliver

Interesting idea. Make use of it rather than throwing it out. Makes sense.

Check out the improving water quality AP 101 Thread

Improving Water Quality

looks like a good way to mineralize the solids.