MKP Mono Potassium Phosphate

[Ca++]

I have some MKP mixed up near it's solubility limit at 20c. Giving me 0-3-3.7 elemental. It's pretty much the numbers I need, but I'm 'afraid' to use it. I see it can make stock tanks of a 0.7ec reading the Yara site. They also say it has uses in hydroponics. However, it's not compatible with calcium. They say it's good to use with calnit, but in separate tanks. I think they are talking as stock solutions, meaning A & B. However it's not clear about what levels A & B can come together, in the final feed tank made up for the plants.
In reality, my feed is one bottle (ionic) containing everything as chelated. That's Ca and P together in my concentrate. So I'm not massively bothered by adding the MKP to a fertigation tank with Ionic, as it seems the Ca is wrapped in this organic stuff, stopping it reacting. I have however, heard of hard water showing precipitation after P was added.

I can't seem to find what I need to know about MKP. I know people are using it though, so I'm looking for some practical examples. I'm using an unknown P and K anyway. I would rather know what I am doing though. Especially having read of people tank mixing extra, to account for precipitation losses(which I can't find now)


Using MKP I can turn my Ionic coco grow into a 200N 60P 250K bloom, which is where I seem to be having the most success. I have been modding the grow for bloom, for many years, but not so cheaply or ideally as MKP could. The Ionic bloom offers 150-60-250 which leaves me low on N. I can't run it higher, or the P gets too much. Though I can use its lower N at the end.
Edit: My K numbers may be off, as these are not that important to me. I just balance them against N, though evidence suggests it's levels are not very important.

 

[jackspratt61]

What ppm Ca you running? Calcium nitrate is compatible with mkp in feed strength solutions

 

[Ca++]

Hey, just the man Impeccable timing good sir.
My taps 280ppm, and my feed offers 80ppm more. I'm usually good between 50 and 80ppm + tap.

I guess the taps carbonate form, isn't the kind of soluble Ca that's eager to wrestle the P to the bottom of my tank. Though people like Harley talk of diamonds falling from solution, with their hard tap water. It's a concern..

 

[jackspratt61]

Your tap will be bicarbonate form unless over 8.3ph or so. Did you test the water?

 

[Ca++]

I had a full suite of tests done. Maybe 100 different things. I just wish I could find it
Probably was bicarbonate, though my pH is right up there. Total hardness was a fair bit higher. My 280 was the calcium part. Now I'm wondering though, I must find it.

I'm sat on sandstone. Ground water here, is second only to the cliffs of Dover. And they have a few inchs of dirt, until you hit solid chalk.

 

[jackspratt61]

Do you recycle your mix?

 

[Ca++]

Do you recycle your mix?

I Just riddle through the coco, to remove most of the roots. I have things I could treat it with, if it was questionable. However, I tend to just get by riddling. The coco turns to some sort of compost over time, but it's weight hasn't been an issue.

 

[jackspratt61]

Mixes become high in bicarbonate as they breakdown. With your water the addition of calcium is working. As the bicarbonate increases you may see P and Mg.

 

[jackspratt61]

Mixes become high in bicarbonate as they breakdown. With your water the addition of calcium is working. As the bicarbonate increases you may see P and Mg.

Sodium buildup in coco is normal. Definitely cause k issues. K + na >10% will block p.

 

[Ca++]

I switched feed to one with higher Ca recently, and saw P problems soon after. Which went when I moved off that feed again. This coco is pretty new, but It's the Asian higher Na stuff, and not getting the runoff it should. So it was combined pressure, stopping the P getting there as it should. I was surprised. It was only 50ppm more Ca, though that's quite a percentage

 

[jackspratt61]

May try .1-.2g/gal MAP in a feed bring up the p and n. Ca/N seems best around 1.2:1 in meqs, in my experience. Ca/p is variable across strains and makes a huge difference in how k/mg is used. Do you have to use ph down?

 

[Ca++]

I use 20% nitric, at 2ml per US gallon. Drops me into the mid 5s, but will settle around 6 given time. It's not an inconsiderable amount of nitrogen, and does me a favour with that tap Ca's availability.
I'm a firm believer in what might be thought of as high N, right through. Running out of every base in the house except miracle-grow, I just finished flowering with 240ppm N into the last week. It's outstandingly high, yet they responded to it quite well

Random tray shot

Dell pulled my monitor off the line and calibrated it in person. There is some flash glare, but that pic (if your monotor is right) gives a fair representation. I would be happier at 180ppm N by later bloom, but I don't chase after numbers below 100ppm and calmag that makes that possible. My grow feed should be used at 7ml/L but I'm using it at 10ml/L to get that 190ppm N. Then adding the P and K, which today I did with MKP. Thanks to your reassurance.

I will look at MAP as I didn't really see it as an N input. Ammonia can't lift the N in my bloom food enough though, as it's pretty bad for yield. Only 5% of N should come from ammonium. By 30% you are really killing your yield, and 50% is outright killing your plants. Though at 0.1 - 0.2g per gallon, you are suggesting a truly small amount.
The Miracle-Gro has a bit too much ammonical N, but I can't say it's impact stood out. Though I had nothing to compare to really, as the whole cycle was using up bit's of feed from about 7 suppliers, that were just cluttering up my place

 

[Ca++]

I couldn't remember before..

MKP makes a 0-3-3.7 elemental PK booster, by mixing 250g in 1650ml of pure water.
0-3-3.7 would say about 0-6-4 on the shelf.

250g is a standard eBay bag weight, and won't stay in solution if you use less water. IIRC if you cool down this 0-3-3.7 to around 10c, the mkp will precipitate, until you warm it up again. I did quite a bit of maths..
If you don't have RO or a distiller, then deionised water for car batteries is usually cheap. In the UK, Halfords sell 5L for about a fiver. That will take 750g of MKP, a Kg of which is £15 (25kg is £40) so it's not exactly cheap, at £20 to make near 6L (buying water, and having 250g spare) but still alright, if these are the right numbers for you.