Comment

Comment by Bob Campbell on July 4, 2012 at 2:22pm

 

Here's a follow up to the idea of using pumice as a grow media.

 

The pumice I bought looks exactly as in this picture.

The size ranges from about  3-8 mm.

The pieces are very hard and do not easily crush.

It's extremely easy on the hands.  It's soft on the skin and nails; not at all like feather rocks or lava rock.  There are no shape shards, and if it broken I doubt that it would become sharp. When it was dry it felt like placing my hands in puffed rice.

The best description I can think of is 'like heavy Perlite'

After soaking for approximately 20 hours about 2/3 sank and the other 1/3 remained floating.  It was easy to separate the sinkers from the floaters.

I would suggest rinsing well as the water was a bit cloudy.

It changed my water's pH from 8 to 6.6

The cost was $28 per 1/2 yard.

I would assume that it is available at many garden nursery suppliers so availability is less of a problem than expanded shale, and yet the price is well below clay medias. 

Overall I think it would be a very good media for ebb and flow if the sinkers were separated from the floaters and some protection were put in place to screen the very small particles.

The material could be separated according to size with a screen, but as is, the particles are probably too small for most net pots. 

For me a lower pH is a plus.  I don't know how that would settle if your pH is already ideal.

I will have to experiment with this, but I think it would be very good if mixed with red lava rock because it would tend to lighten the media so as your hands move though it would yield easily.  But the extra weight of the red lava would help stabilize the plants.

Comment by Bob Campbell on July 4, 2012 at 12:25pm

Yes the problem is without a doubt solved.  The plants are growing much faster and very green now.  What a difference!

Thanks for the definition of RSG and the link.  I never would have guessed that one. 

Comment by Jon Parr on July 4, 2012 at 11:57am

Yeah, Bob, no worries. It may very well have been an iron def., it just didn't look like it in the pic, to me. Either way, problem solved, eh?

Comment by Jon Parr on July 4, 2012 at 11:52am

RSG stands for "really smart guy", and is discussed here: http://www.backyardaquaponics.com/forum/viewtopic.php?f=8&t=2173

(Although I believe it was started on an earlier thread) Basically, the attempt is to replicate how iron is made into plant usable ferrous ions in nature as it turns out, iron deficiencies are rare in soil, and this is because ferrous iron is produced by anaerobic bacteria in the presence of carbon. Of course, anaerobic conditions are discouraged in AP, and hence a notorious lack if ferrous ions. My take on the RSG morphed into a trough filled with sand, iron fines, charcoal, and some clams, beneath a foot or so of slow moving baffled water to allow settling of solids. Knowing what I know now, I would place a bunch of bird netting and gammarus in the water above the clam bed, an let thus whole thing be a nutrient factory between FT and GB. The idea behind the clams is that their movement would periodically move sone anoxic ferrous water into the flow of water going to the GB, theoretically.

Comment by Bob Campbell on July 4, 2012 at 11:44am

@Jon - I still don't think it was an iron deficiency that the basil exhibited. Perhaps magnesium? Perhaps the abundance of iron freed some magnesium or other minerals in your system, after all, iron is not the only cation used in CEC, right? I'm just wondering if some Epsom salts, or even some seasalt, would have been better to add than an excess of iron phosphate. Just sayin'.

You may be right.  The problem began to clear up after switching to Dr. Iron, but I did add Epsom Salts while the plants were beginning to look better.

That was not very scientific of me, but it seemed at the time a good idea,  because I it appeared to me that the iron had fixed the problem. 

Comment by Jon Parr on July 4, 2012 at 11:20am

Thanks for that "iron cycle" in layman's terms, Vlad. Love it. Btw, did you ever build the RSG V.2? I was all staged to do it, but got discouraged when I learned how shortly lived the the potential iron would last, and a bit worried that the Fe3 created would build to toxic levels for the fish. I had my RSG positioned after FT, before sump, then sump to GB. I was torn whether or not to aerate sump for the benefit of the GB, or pump anoxic ferrous water to the GB's. The UVI model uses a baffled settling tank (no air), then a bird netting "mineralization" tank (no air), then a degas tank (roiling air), then DWC. Part of the reason for degas is hydrogen sulfide removal (I think), and apparently much of the nitrogen from ammonia is converted to atmospheric N3 during the anoxic stage. Assumably, then, the UVI model likely has available ferrous iron before they boil it with air. Seems like the better place for the degas tank would be the DWC itself. Perhaps the best place for the RSG filter is simply at the bottom of the GB's or DWC? I think is was Peter Shaw that mentioned some experiments where the solids were pumped to fabric tubes laying on the bottom of DWC. The solids were trapped in the tubes to further mineralize in anoxic water, and the water joins the aerated DWC. Hmm

Bob, thanks for clarifying the high DO in your DWC. I understand that adding iron eventually cleared your deficiency symptoms in your basil, but I still don't think it was an iron deficiency that the basil exhibited. Perhaps magnesium? Perhaps the abundance of iron freed some magnesium or other minerals in your system, after all, iron is not the only cation used in CEC, right? I'm just wondering if some Epsom salts, or even some seasalt, would have been better to add than an excess of iron phosphate. Just sayin'.

Comment by Bob Campbell on July 4, 2012 at 11:10am

@Vlad - THANK YOU! 

I must be driving you crazy with my inability to grasp the concepts involved but I think I've got it.
Just to be sure let me restate what you have told me.

I'm getting that a lower pH is required for FE2+ uptake by the plants because the organic acid (the chelating agent) keeps the FE2+ bound in that ferrous state long enough for the plants to utilize it. 
Otherwise the ferrous iron will begin to precipitate out of solution and stick to the rocks and walls of the tank.

Chelation does not involve a transfer of electrons, but instead it is the ability to bind the iron compound in the ferrous state.

I'm also getting that a low Oxidation Reducing Potential will tend to unbind the ferrous FE2+ and allow the compound to transition into a ferric FE3+ state because of the availability of oxygen. 
Whereas a high ORP with organic acids will act as the chelating agent binding, and keeping the iron soluble and non-reactive with the oxygen.

Did I finally get it?

I should probably just stop here, but if I been a good student, and if you have the time I have a couple other questions.

I'm also getting that the ferrous and ferric transition is REDOX, and that the compounds are in different states if oxidation.
Can inorganic acids also act as a chelating agent?  If the acid is organic rather than inorganic, what is the reaction?
I'm not sure but I'm guessing the oxygen is more available when the ORP is low because of excess hydrogen ions or hydroxide ions which would react with the FE2+ if an inorganic acid were present.
or maybe because it too has a positive ion charge.

Also what is an RSG filter2.0?

Comment by Vlad Jovanovic on July 4, 2012 at 10:23am

hmm...define "organic". If you mean something like the "Organic Based" 10% Iron Chelate product that is sold on this site...No, you can't make that at home. If I recall, that product is is a run of the mill EDTA chelate...And use of the word "Organic" in the labeling is run of the mill marketing (iron chelates are ok for use in some countries in organic food production so that word gets thrown around a lot, creatively at times).

Bacterial siderophores redoxing and chelating iron, like Bob alluded to, can be thought of as an organic iron chelate I suppose...

Iron chemistry is kind of a tough one guys, because it's behavior as a transitional metal, and it's willingness to complex easily with just about any other substance, it gets a bit complicated...(relative to say adding potassium, or magnesium or whatever)...but, yes I feel it can be done. Just not very easily.

It's been gone over a bunch here, strewn about in various threads on the site (you can search for them) or start with RSG filter conversations over at BYAP. Again,(iron cycle and it's manipulation) it's not a 'quick and easy' type deal, and would probably entail as much research and tinkering as AP (nitrogen cycle and it's manipulation) itself. But some folks like that kind of stuff

Comment by joe on July 4, 2012 at 9:43am

Hi Vlad,

Do you know how organic iron chelate is made? Would it be possible to make at home?

Comment by Vlad Jovanovic on July 4, 2012 at 1:09am

When time has gone by, you are feeding your fish a proper diet, you are keeping your pH within proper ranges, and/or you are adding chelated iron (iron in the range of 2-3ppm should be alright) you will, I'm betting have enough iron (or whatever) in solution so that your medias CEC will not really matter...

It only serves to explain why in peoples mixed/hybrid (DWC and Media bed) system at a particular point in time, and/or under particular circumstances (like low nutrient availability in solution for whatever reason, and there could be a number of them, crappy fish food, under fed, under stocked, brand new system, high pH, blablabla)...

the DWC sub-system may exhibit deficiency symptoms before a media bed will. 

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