I have some masdevalias and some other light feeders, but I don't mix weaker nutrient solution just for them. I use only inert medium for them and I keep them on the wet side to prevent the nutrient solution to concentrate itself (evaporation).

Shelf life is of no concern as long as you shake it before dispensing to make sure it's homogeneous, and keep it closed to prevent evaporation between uses.

If 500 g of powder will make 526.32 L of 125 ppm N solution, a 100:1 concentrate would be 500g powder to make up 526.32/100=5.26L, not 9L (which would be a 58.444:1 concentrate).

How does the inert medium play a role? Bark, or similar media components contribute nothing the the concentration of nutrients - unless they are decomposing, in which case you'd better repot anyway.

I understand the not letting the solution concentrate by evaporation, but don't see a difference based upon medium.

So if i mix 500g in 5.26 L , how much feed IN ml per litre of water is required for 125 ppm N ?
Am i right with 11 ml per lt?
Were did 58.444 come from ?

Sorry Ray i was associating text in brackets to 5.26 lt not 9lt.
So i need 10 ml per lt as the 500g in 5.26 lt makes a 100-1 concentrate .

Let's look at it in mass, like it's supposed to be. I hope this doesn't confuse things.

■The fertilizer is 13% N, so the 500g of powder contributes 500 x 0.13 = 65 g N.
■A ppm is the same as a mg/kg
■If your final target is 125 ppm N, that's the same as 125 mg/kg of solution.

Let's also be clear of something here: that measure is 125mg per kilogram of solution, not added to a kilogram of water.

If you want a 100-1 concentrate therefore, it must contain 100x that amount, or 12500mg (or 12.5g) of nitrogen.

If we add 500g of powder to 5.26L (5.26kg) water, our solution will end up with 65g N in 5.26 + 0.5 = 5.76 kg of solution. or

(65g N x 1000 mg/g) / 5.76kg = 11285mg N/kg solution, which is slightly more dilute than the 100:1 concentrate you targeted - 12500mg/kg.

I'd still use 10 ml / L for my final mixture, however, as the 10 ml is NOT 10g, due to the slightly higher specific gravity of the solution compared to plain water, and it's bloody well close enough!!!

Where or how do you know that the feed = 0.5 water when adding the feed TO water ?

You're trying to achieve 125 mg of N for every kg of SOLUTION, not of just the water in the solution.

If you added 500g of powder to 5260g of water, your total for the mass of the solution is 5760g. Simple as that. Your concentrated solution, as I said, is now 11285 ppm N.

I don't know the specific gravity of such a solution, but you KNOW - because it contains some dissolved solids - that it will be higher than 1.0, the sp. gr. of pure water. As we don't know the correct value, we can simply accept 1g/ml.

Using the 11285 ppm N solution, we know that 10 ml will contain 112.85 mg N. If we are willing to accept that the concentrate is 1 g/ml, then adding 10 ml of the concentrate to 1 liter (1kg) of water means that the solution will be 112.85mg N in 1010 ml (1.01kg) of solution, or 111.7 ppm N.

Use it and stop fretting over such details. Your plants are sitting there hungry while you do the calculations. :rofl:

What orchids ,they are dead through starvation :D

I will be happy when i have got the solution right @ 125 ppm /mixing with my eyes shut :biggrin: plants doing better than ever in six months time , then i can sit back and trust the MSU formula :bowing please fingers crossed !Until then i am learning for myself .With some fab advise :thankyou
Good or bad this thread will be updated .

I am not 100% confident that 125 ppm N will not harm my Masdevallia/Restrepia ,Disa or make them do better than a weaker feed .
I was feeding at two different strengths for My Massies 100 ppm N and others 125 PPm.
But got tired of having two lots of water storage containers to hold the feed etc Hence the feed all at 125 ppm N.
Some Masdy leaves are distaughted but don't know if this is feeding or another problem.
I have decided i am going to feed ALL my orchids at half the 125 PPM N target at every watering with no flushing.
If it wasn't for my Pleuros then it would be 125 ppm but these take priority over the rest of my collection and hopefully this will still be enough for them all .
I am giving them this summer and into autumn then i will review how they are doing .
Oh i have a Masdevallia that is going to be used as a test plant and will be hit with 125 PPM N just to see any differences .Not scientific i know but i will be able to see if roots and leaves are good etc .

I have change my mind again and going for 3/4 of 125 ppm for all my collection so approx 94 ppm N .