Aquaponic Gardening

A Community and Forum For Aquaponic Gardeners

If you are growing using Flood and Drain on a timer, how often to you cycle and for how long?  I think most of us use 15 minute interval timers, so I'm guessing that the duration of a cycle is typically 15 minutes - I know mine is.  I tend to go 30 minutes between cycles if everything is nicely balanced and only 15 minutes between if I'm overstocked with fish and need the oxygen more than the plants need the dry period - which is where I am in 2 out of 3 of my systems now.  The other data point I have is Joel at Backyard says he typically goes 15 on / 45 off with his systems. 

What do you do?  What have you found works best, and what just doesn't work?

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Yep, oxygenation is the key... even in NFT and raft systems IMO... although raft systems can get away without supplementary aeration ... if the flow/turnover is high enough.. and/or the rest of the system is well oxygenated...

Murray,

 

I sent you an email about two or three weeks ago asking about the 3/4" gravel you are using.  I haven't received your answer and think it may have been lost in the mix.  I initially used a 3/4" gravel that looked identical to the gravel you used in your DVD.  However, I found the gravel here was from limestone and wouldn't allow my ph to fall below 8.0.  I assume the gravel there is of a different composition.  If so, what is the composition?  Is it granite?  A bigger problem is that after carefull research, to determine if red lava rock would contain mercury and found it would not, I tried a growbed with red lava.  I'm still getting ph levels of 8.0. after carefully cleaning out anything that came in contact with the limestone.  Do you have any ideas of why I can't seem to lower the ph levels?

 

JoeJ

Murray Hallam said:

Hi John,
I have the utmost respect for Joel as you know, but I would not rush in and come to conclusions on such a short trial.  We ran ours for 6 months or more. I would have to look back into my diary to see just how long, but it was at least 6 months.

Things change over time.  With our trials on continuous flow, we found it only worked if run with Hydroton or CANNA clay pebbles.  Did not work very well at all using good old 3/4" gravel.   Hydroton and the like allow for a bit of "wicking" effect to spread the moisture around the grow bed.    Also, delivering the water over the pebble surface by the distribution grid promotes water loss via evaporation.  Not important in a mild climate, but in a hot arid climate this would be a major factor.

Just a few more thoughts to share...

Run some tests on your tap water.  And keep in mind that immediately out of the tap the water will probably have a false low pH reading.  You need to let the dissolved CO2 outgass before you can get an accurate pH reading on tap water.  Most tap water actually has a relatively high pH if it comes from wells in a limestone aquifer.

 

This high starting pH will come down over time if there isn't anything else in the system buffering the pH up but it can take a while.  I have in the passed used acid to bring my well water pH down to 7.6 before starting cycling in a new system and as the system cycled up the pH dropped more and I did even have to add some buffer back into the system.  So it may be worth testing your source water for pH and perhaps even alkalinity.

Perhaps with drawings!

Chris Smith said:
There seems to be so much confusion on terminology it might be best if we make an  "aquaponics definitions" page to go along with "what is aquaponics" and "rules of thumb" on the home page.

In my group I've re-posted a bunch of my drawings and here is another link to find them as well


Useful Diagrams


Joseph Orlando said:

Perhaps with drawings!

Chris Smith said:
There seems to be so much confusion on terminology it might be best if we make an  "aquaponics definitions" page to go along with "what is aquaponics" and "rules of thumb" on the home page.
Hi Joseph,
the composition of gravel differs from location to location here in Australia as well.  I should have made that clear.
Usually a talk with your gravel supplier will reveal the composition, especially be aware of limestone.  Sorry for the difficulty that has caused you.
Trouble is, different areas apply different names to gravel types.  We have here in Queensland what we call "blue stone" which is a basalt type rock crushed and usually used for road construction. It is just great for our purposes.  Another type that can be purchased her is termed "drainage gravel" It is also fine, in my area.   Other parts of our state it has limestone in it.  All depends on the location of the quarry they get it from.
Of course, Hydroton or CANNA clay pebbles are just great and safe, If you can afford them.....

Joseph Orlando said:

Murray,

 

I sent you an email about two or three weeks ago asking about the 3/4" gravel you are using.  I haven't received your answer and think it may have been lost in the mix.  I initially used a 3/4" gravel that looked identical to the gravel you used in your DVD.  However, I found the gravel here was from limestone and wouldn't allow my ph to fall below 8.0.  I assume the gravel there is of a different composition.  If so, what is the composition?  Is it granite?  A bigger problem is that after carefull research, to determine if red lava rock would contain mercury and found it would not, I tried a growbed with red lava.  I'm still getting ph levels of 8.0. after carefully cleaning out anything that came in contact with the limestone.  Do you have any ideas of why I can't seem to lower the ph levels?

 

JoeJ

Murray Hallam said:

Hi John,
I have the utmost respect for Joel as you know, but I would not rush in and come to conclusions on such a short trial.  We ran ours for 6 months or more. I would have to look back into my diary to see just how long, but it was at least 6 months.

Things change over time.  With our trials on continuous flow, we found it only worked if run with Hydroton or CANNA clay pebbles.  Did not work very well at all using good old 3/4" gravel.   Hydroton and the like allow for a bit of "wicking" effect to spread the moisture around the grow bed.    Also, delivering the water over the pebble surface by the distribution grid promotes water loss via evaporation.  Not important in a mild climate, but in a hot arid climate this would be a major factor.

Just a few more thoughts to share...

How about using good old river gravel in the bottom part of the grow bed and topping it off with Hydroton to achieve a wicking effect? It seems like this would help offset the cost of Hydroton thoughout the grow bed, but also offer some of the wicking advantage.

 

Brian

Murray Hallam said:

Hi John,
I have the utmost respect for Joel as you know, but I would not rush in and come to conclusions on such a short trial.  We ran ours for 6 months or more. I would have to look back into my diary to see just how long, but it was at least 6 months.

Things change over time.  With our trials on continuous flow, we found it only worked if run with Hydroton or CANNA clay pebbles.  Did not work very well at all using good old 3/4" gravel.   Hydroton and the like allow for a bit of "wicking" effect to spread the moisture around the grow bed.    Also, delivering the water over the pebble surface by the distribution grid promotes water loss via evaporation.  Not important in a mild climate, but in a hot arid climate this would be a major factor.

Just a few more thoughts to share...

If you are flooding and draining or running constant flood, the wicking effect is not necessary.  (constant flood being different than constant flow just in the bottom of the bed but the clay will only wick up to a point, probably a few inches max.)

 

Anyway, as to using river gravel in the bottom of a bed and the clay for the top several inches is an idea that people Have used and liked.

 

Keep in mind that wicking doesn't give you filtration.  You need to flood or flood and drain to get the benefit of bio-filtration of the media.

TC said: "Keep in mind that wicking doesn't give you filtration.  You need to flood or flood and drain to get the benefit of bio-filtration of the media"

Great observation TC. In this way I won't underestimate the media/fish ratios and "under" filtrate.

 

Hi guys.  I'm not understanding what you mean by "the wicking effect".  There is no wicking done by gravel or Hydroton, to the best of my knowledge.  Am I missing something?

 

signed...confused and bewildered 

Cant tell you how valuable these discussions are to new grower like myself. It clearly shows how young this new industry is. It also shows the new guy how he can set up and run a multitude of ways and make it his own. Great conversation.
Sylvia, Hydroton does have a wicking effect as TC has stated, but it is only a few inches.  I actually start my seeds by driect seeeding them in net pots filled with only hydroton.  The net pot are set in standing H2O to about 1/3 of the height of my net pot. In a little while the entire pot of hydroton will be moist through the "wicking effect".  I have noticed also when i run my setup without lights the hydroton on the top of my growbeds become moist through wicking (even though my overfow is 2" below the surface of the hydroton), but soon after i turn the lights on it dries out the top 1".  Hopefully this makes some sense; i have been using hydroton for almost 4 years now and it does have a small ability to wick.

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