Aquaponic Gardening

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Have had pretty good luck growing must things except root vegtables. Radishes are okay, but not great. Same with carrots. From growing in soil I know it takes the three main things to be balanced. Nitrogen, Potasium, and pot ash. Plus other things like Iron. In aquaponics, nitorgen usualy isn't an issue, due to what the fish provide in the water. plus I add Iron chelate occasionly. But what are the thoughts on adding potasium, and potash. If I rememeber, if pot ash is down, root vegitables do not do well. Of course then there's the thought is we start adding chemicals, we're not into "true" aquaponics, it's more like hydoponics. All thoughts and oppions welcome

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What kind of system are you running? Media based? DWC? NFT? If you're doing media, you may have a harder time with root vegetables. The veggies have a harder time pushing through the media and you might get some funny shapes.

What radishes and carrots I've gotten are fine shape wise. That's not the issue, they just don't get big, and I think it has something to do with nutrients. I use pea gravel. Going to re-check my PH, I hear, if that';s off much, it can lock out nutrients

Mike, how old is your system, what ammonia did you use to cycle it and what do you buffer your pH up with?

Pot ash is just the old english/american name for potassium, so they are in essence the same thing (i.e Carbonate of Potash [Potassium carbonate], Muriate of Potash [potassium chloride], Caustic Potash, [potassium hydroxide] etc...most everywhere else it's called by it's Latin derivitive, Kalium hence it's K on the periodic table of elements. The three major plant essential elements are Nitrogen, Phosphorous and Potassium (N-P-K)...Anyways...

It's not likely AT ALL that you'd be experiencing pH related Potassium (K) lock-out. That type of thing doesn't really happen with K. Things like Iron, Boron, Zinc sure (and maybe Phosphorous to an extent, but not likely just by the sheer amount in solution that fish effluent would provide), but not Potassium.

It is much more likely that there is not enough K in solution, in your system (it's probably less than a few years old, you probably cycled with pure ammonia instead of something like humonia which has the benefit of added trace and other elements [like Potassium], and you are probably buffering your pH with a calcium based buffer (be it through CaHCO3 hard top-up water, shell grit, or builders lime or whatever).

Of the major plant essential elements Potassium is the weak link is a fish poo based system like AP. That's just the way it is...Which is why many if not most aquapons use a potassium based pH buffer (alternating with a Calcium based one).  The easiest thing to do to add K is buy some Potassium Bicarbonate (KHCO3) to buffer with. Or, if your pH is already high due to the calcium carbonate in your source water...then salt your system (for fish health) with Potassium Chloride (KCl). I make my own Potassium Hydroxide out of nothing more than wood ashes and rain water, it works great to raise pH but it's really strong stuff and can mess you (or your pH) up right quick if you are not careful.

Potassium Bicarbonate is probably the easiest (and most forgiving if you fuck up and add to much or spill some or whatever) way to add K and buffer up your pH at the same time. Again, if your pH is already high use some KCl. Or, if you happen to live by the sea on a clean stretch of Ocean...use a bit of seawater or collect the salt of the rocks...there is plenty of Magnesium (Mg), Potassium (K), and a host of other trace elements in there as well.

If I have to do anything to the pH, its usually having to add acid. System is about a year old

2 much N

Izzy, it's really not as simple as saying "too much Nitrogen". While Nitrogen in the form of NH4 (ammonia) does behave antagonistically toward other cations (particularly Potassium) and can lock K out. Nitrogen in the form of NO3- (nitrates) does not...at all exhibit this antagonistic behavior toward K or any other base metal cations. And I'm guessing that Mike's NH4 is not "off the chart" (or his fish would be dead) and that most of his N is in the form of NO3-. And again, "too much" NO3- is not going to be able to block out Potassium.

Mike, since you usually have to add acid to your water, that means that your cabonate hardness (usually in the form of calcium carbonate/bicarbonate [CaCO3]) is high. So up till now your buffer has been a calcium based one. (as a side note, too much calcium can and does block out potassium uptake...this can usually be remedied by adding potassium, rather than trying to remove the calcium, so don't worry...it's more of a balance/ratio type thing). This is one more "strike" against potassium you have going in your AP system. The main one though is that fish effluent is just not being able to at this point, provide for the potassium needs of your root crops and/or heavy fruiting plants. If you have your feed analysed, then analysed your fish poo, then compared that to the needs of heavy fruiting plants or root crops you'd see that. But there's no need to as others have already done that...This coupled with your hard water/calcium situation (every time you add acid to your top up water you are neutralizing the CaCO3, by doing so the calcium carbonate dissociates into Ca2+ (which is plant usable calcium) and some CO2 gas...This is good if you are 'low' on Ca in a system, but bad if your already thin on K...Like most new AP systems are...unless the operator has intervened...

If you want the easy, fish safe (actually fish beneficial) non-pH raising way to add a bit of potassium and watch your root/fruiting plants take off... get some KCl (potassium chloride) it's often sold as a water softener salt for drinking water, or as a dietary table salt substitute for people with high blood pressure who have to avoid regular sodium salt (table salt NaCl). Get the stuff with no anti-caking agents or iodine added and let me know how much total water is in your system and I can help you figure out how much to add to get to 250-300ppm if you want. 

I have pretty close to 1200 gallons

1200 US Gallons is 4542.49 liters (we'll call it 4500)

So 4.5 kilograms of KCl would be 1ppt...half of that, so 2.25kg would be 500ppm and half of that would be 1.25kg=250ppm

So 1.25kg of KCl. That's 2.75 pounds. So about 3 pounds of KCl should do it (250-300ppm). You could double, or even triple that amount and you'd still be fine. (It might be pointless, and a waste, but you wouldn't be harming fish, plants or bacteria)...

Dissolve it completely in a bucket and and just add it to the sump. Or, half in the sump, half in the FT or a little at a time over the coarse of a couple hours...whatever... it really doesn't matter much as long as it's dissolved well. What you don't want is a big chunk of un-dissolved salt sitting in the FT is all. 

3 lbs. No iodine, no anti-caking agents (actually 2 of the 4 types of anticaking agents are just fine, while 2 are questionable. If you can't find any without those additions, again let me know what is available to you and we'll work it through. But basically anti-caking agents listed as E535 or E536 are the questionable ones, while E504 which is just magnesium carbonate, or E170 which is calcium carbonate are both fine...and actually beneficial.

@Vlad: nope

@Mike: 2 much N

@Vlad: SPOILER ALERT: (also, you seem to misunderstand the interaction between divalent cations and monovalent cations competing for uptake to plant roots capable of selective permeability, especially given the pH conditions... I'm not going to get into here but your local community college should have some courses on the subject or faculty from your local extension can help fill in the gaps of knowledge... the crux of the issue lies in plant metabolic processes NOT the activity of chemical species in the water, don't give up on learning; you clearly have a talented mind and a passion for this stuff)

Right Izzy. You caught me. I'm just making this stuff up...

"The crux of the issue" is Mike's stated need to add some plant essential elements (in this case K) in a manner that will not affect his pH.

Selective permeability doesn't mean much when there's not enough in solution to 'select' or 'permeate'.

And what would you have Mike do? Take out some fish to lower N...Or perhaps add more plants to use up some of those nitrates? Neither seem like a particularly useful strategy. I fully stand behind everything I've said about increasing the amount of K which is present in solution as a remedy. 

Please enlighten me on my "seem(ing) to misunderstand the interaction between divalent cations and monovalent cations competing for uptake to plant roots capable of selective permeability, especially given the pH conditions." as it pertains to the OP, or anything that I've stated here. It will save me a trip to the 'local community college'.

I thought the deal was that root veggies will grow in an AP system but will come out in wonky shapes because the media isn't as forgiving as soil is. So far I have tried radishes and they didn't do anything. They sprouted then yellowed and stunted as wee sprouts for the last couple of months. I believe that it is because my system is young and has not developed the P or K concentration needed (like you say) for root vegetable growth. How old is your system? From what I remember reading Aquaponic Gardening your system needs to be something like six or eight months old before it has the right concentrations of nutrients to grow anything other than leafy greens.

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