Do liquid ferts (NPK) deteriorate over time? - The Planted Tank Forum
 
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post #1 of 8 (permalink) Old 10-26-2011, 03:40 PM Thread Starter
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Do liquid ferts (NPK) deteriorate over time?

I use dry ferts and make my NPK mix for EI dosing, but I only make two weeks worth at a time...mostly because I have some feeling that the efficiency of the ferts when mixed in water will deteriorate over time. Is there any truth to this? (fyi: I prefer dosing in liquid form instead of measuring different fertilizers with teaspoons every morning...just saving what precious time I have before work)

Ideally, I'd rather mix up a batch that will last me a few months at a time.

(I do however use pre-mixed CSMB which lasts forever)

So, is it OK to make a bigger batch?

Thanks!

65g planted tank - 200W heat - PC 192W/6700K - Eheim 2217 - Pressurized CO2 - EI Dosing
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post #2 of 8 (permalink) Old 10-26-2011, 04:29 PM
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Not without a nuclear power plant involvement. NH4 might go to NO3.........or Fe might become unchelated etc...but the ferts themselves are stable. In liquids, they can mold etc.........but dry they should last much longer than we do.




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Tom Barr
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post #3 of 8 (permalink) Old 10-26-2011, 06:22 PM Thread Starter
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Thanks Tom. I'll put a splash of Excel in my big-batch NPK, just like I do with the CSMB to avoid any mold.

65g planted tank - 200W heat - PC 192W/6700K - Eheim 2217 - Pressurized CO2 - EI Dosing
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post #4 of 8 (permalink) Old 10-26-2011, 09:56 PM
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I've never made liquid ferts, but from what I've seen I think you'll be OK for a few months. I do know that preservatives are added to liquid ferts (like Rootmedic's), though I don't know the science behind it.

I do believe that ferts like those will keep for 1 year+, which would not be possible without the preservatives.


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post #5 of 8 (permalink) Old 10-26-2011, 10:48 PM
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Without preservatives liquid ferts get mold pretty quickly. Excel(glut) is the easiest if you have it at home. However, if the bottle is clear and exposed to light/opened often, the glut will degrade quickly and even then could start growing mold after 4-5 months. This is why rootmedic now uses food grade preservatives.

In some solutions, mixed at the max concentration they can become unstable over time and a little falls out of solution, but the ferts are still bioavailable... just in salts.
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post #6 of 8 (permalink) Old 10-26-2011, 11:05 PM
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This is from other forum that I've been using for my EI dosing. I mix NPK in one 500 mL bottle and CSMB in other 500mL. And I do keep my trace mix in the fridge. So far I had no problems.

"Potassium Nitrate - 40g to 500ml of water and adding 10ml per 100L of water would give you a value of 5ppm.
Potassium Phosphate - 15g to 500ml of water and adding 5ml per 100L of water would give you a value of 1ppm.
Potassium Sulphate - 55g to 500ml of water and adding 10ml per 100L of water would give you a value of 5ppm
Magnesium Sulphate - 70g to 500ml of water and add 50ml once a week per 100L of water - this would give a target of 7ppm.
Trace mix - 15g to 250ml of water will give you about the same concentration as the ‘off the shelf’ products. It is also a good idea, if you can, to add 0.5ml Normal hydrochloric acid as this helps to prevent the chelator from breaking down. Some people complain of mould growing on top of the solution - keeping it in the fridge should help prevent this and prolong it’s life.

It is possible to add the solutions into one bottle except for the trace mix as, depending on the chelator used, the iron could react with the phosphate. Generally speaking it is a good idea to make the solutions up in separate bottles until you are comfortable with the dosing.

nb. It is preferable to make up the solutions in RO water or Deionised water, but tap water can be used if need be."
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post #7 of 8 (permalink) Old 10-27-2011, 02:06 AM
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Fertilzing can be done very simply, or it can be done so it is like playing Chemistry lab technician. If you enjoy the latter approach, do the chemicals in separate liquid mixes, using distilled water, and a microbalance so you know very accurately how much of each you are dosing. But, if you prefer to make it simple, just follow the EI method, described in the sticky, and, if you want, premix everything except the trace element mix and chelated iron, if you use it, in one bottle of tap water, using measuring spoons, and the traces and iron in another bottle mixed with tap water, and measured with measuring spoons. To make it even simpler, use a 64 ounce dosing bottle, put 64 times each of the amounts the table recommends per dose in the bottle, and fill it with tap water. Then dose one ounce per dose.

However you do it, it won't be wrong. It's up to you to decide what you enjoy doing.

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post #8 of 8 (permalink) Old 10-27-2011, 03:28 AM
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No not really. Although I do use formaldehyde, HCL and quinine in mine lol.
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