Backyard Aquaponics
A place to discuss aquaponics

Its pretty common for many AP systems to need Potassium (K) supplementation but how do you add it.

Banna peels and the like aside there are generally two ways that are commonly talked about and used.

Potassium Hydroxide (KOH) and Potasium Bi-Carbonate (KHCO3).

As far as I know there are a couple of major pros and cons.

PRO KHCO3 will shift the pH toward alkaline and the bicarbonates will also buffer the system creating a more stable pH.

PRO KHCO3 can be used as a fungicide and foliar feeding spray, I don't know if KOH can or not but I suspect not.

CON KHCO3 costs a lot more.

PRO KOH is cheap.

CON KOH is very alkaline and it would be easy to make a mistake and shift the pH to far and stress out (read kill) fish.

CON KOH Will not buffer your pH so any shift in the pH may be dramatic and shortlived. Not necessarily a problem if you have something else to buffer the pH.

The cost of the two materials varies but a quick google gives prices for KOH at around $15/kg and KHCO3 at around $20/kg although the name brand ECO-Rose is sold for $20/500g.

That might not seem like that big difference but when you actually translate that into how much K you are actually buying as distinct from oxygen (O), hydrogen (H) and Carbon (C) it works out to be $21.5 per kg of K when buying KOH and $51/kg of K when buying KHCO3.

I'm sure I've missed a few things but I'm about to order several bags of stuff and the difference between the KOH and the KHCO3 got me thinking. So I did the maths on what was the real cost of the K. I think I've be going with KOH and I'll buffer with Calcium Bicarbonate.

I just got a cheep bottle of tomato feed? Made by Manutec.
N.10.0
P.2.0
K.9.0
MG.1.5
CA.2.5
1kg $7.
Only been using it a week now, just the one tomato due to the rain we had, even the plant pots took a hit. Bloody global warming! I may have to invest in an umbrella shop? To stop the rain.

Thanks for the info Stuart, I haven't paid a lot of attention to supplements yet so it's nice to see a concise opinion.

Do you have a test kit Blizzard?
I'd be interested to know if the N in the tomato feed shows up as ammonia, nitrite or nitrate.
Cheers.

I use KOH because I needed the pH raised and K supplementation. I use roughly the same quantity of KOH and ag lime (by volume as in several serving spoons of each at a time, obviously will depend on yr system).

This system is working for me at the moment. One prob I have with KOH is that even though I was storing my 20kg bag in a screw too bin, it still absorbs enough water to turn it into a solid block so I need to chip away at it to get some. Little dangerous cause I'm generally not wearing gloves or goggles at the time.

Have thought of turning it into solution to make it easier but it is extremely exothermic and as such I'm hesitant to do it.

Dumb question but I was wondering, is all Potassium Bicarbonate the same?

I was looking for some to use mainly for pH adjustment rather than supplementing and came across a couple of chemical suppliers that seem to supply the wine making industry. Their prices seemed good ($10-13 per kg before shipping, so it may well go up heaps) but I am not sure if it's the same product that can be used in AP?

On the sites I saw they just listed it as Potassium Bicarbonate KHCO3, so is it safe to assume it's pure and safe to use?

http://www.enoltech.com.au/products/win ... onate.html

http://www.anpros.com.au/wine-making-pr ... carbonate/

Yes I do. My nitrates at the last two test were around 8. that’s why I put in the tomato and cucumber plants, as well as a chilly and capsicum plant, with the other plants including 3 types off basil,

Ammonia and nitrite levels are zero! ATM. Fish are getting fat!!!!! Especially one delicious looking silver perch around 40cm. I don’t think I will get them next year not that I wanted them this year, as they are too skittish and are upsetting the Barra! After going to several shops after food for plants in aquaponics and looking on websites. I have found F**k all! Available! So after reading a lot I found this brand to be the best I could find. Unless you can recommend another,

I am new. I am learning. But I am not getting any real answers so I have gone my own way. My fish are healthy. Plants are doing good. Filters are working fantastic!
The problem I see is the experts on here all have bigger shop systems or they are selling systems, are giving the wrong advise to the real backyard novice like me.

sigh... I asked you that because I was trying to help you join in with happy, reasonable discussions now that you're back on the forum. (and because that product contained nitrogen which I personally wouldn't really want to supplement my system with but thought I'd mention it obliquely so as to not incur wrath...)
Please don't keep banging that old drum man.
Everyone knows where you stand, we can all give advice based on our experiences and we aren't all going to agree. There is no need to take it personally when someone else has a different view and it gets old hearing about it almost every time you post (whether it is on topic or not).
Don't hate me, trying to help here...

My question, how much potassium should we have to keep an all rounder system? So without everything bolting, but fruiting plants putting out lots of flowers?

And what's the best way to test how much potassium we have in our systems?

I think mine is off the charts due to some snail baits I used, tomatoes are going nuts and putting flowers on small plants, and everything else is bolting. I'm hoping that the tomatoes will suck it all out soon, so my new batch of lettuce won't bolt straight away.

I use KOH and Ca(OH)2, typically been using 50% KOH solution in 50-100g quantities, and Ca(OH)2 (powder)in 15-20g additions when the fish are eating a lot, neither of which results in large pH swings,and I also have a lot of CaCO3 in the GBs. There is no danger of wild pH swings if you don't go beserk and throw in a huge amoount of alkali! Use a pH meter to keep an eye on it. I have ~6000litres of water in my system, and fish eating a lot means 300-500g pellets per day.

The Horiba potassium pens have been recommended before.

They are a bit pricey but I don't like reagent tests. $372 from their Australian rep.

With the horiba pens, don't forget to include the cost of calibration fluid (it has to be calibrated every time it's turned on), and replacement sensor heads.

The LaMotte 3138-01 is a pretty good test kit for potassium - i picked mine up for $65.

If ph is high I use Potassum sulphate, otherwise potassium bicarbonate.

Didn't think high K would cause bolting, thought that was more phosphorous? Which snail pellets contain K Colum?

I looked in to buying the lamotte kit here in aus but the supplier wanted $150!! Would love to pick one up for $65, though AFAIN you can't ship it from US to Aus due to corrosive chemicals and airmail restrictions. Would love to get a test kit as I think my systems are often low in K. Note you will get reduced productivity with low K way before visual signs of deficiency.

At risk of going off topic, I also supplement Phosphoruous using phosphoric acid in summer (to address high ph top up water) and rock phosphate in winter. I've been testing my phosphate levels and have yet to see a reading in an un supplemented system - even after a season of trout and 150g/day I still had no phosphate reading. It might pop up eventually (systems are 18 months old), though I would expect to see some P due to solids mineralisation by now! I tend to only supplement the heavy fruiting systems though, my greens system does not get it due to bolting issues.

What phosphate test are you using?