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Dry dosing NPK

MichaelJ

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Hello,
I am switching over to dry dosing NPK in my two low-tech tanks and trying to figure out what compounds to use. I am actually not going to dry dose Potassium (K) as I am using Potassium salt in my house hold water softener so my Tap / RO mix contains a lot of K already. So for Nitrate I want to avoid Potassium Nitrate KNO3 as I don't need the K (I know it probably wont hurt, I just don't see any reason to add more if I can avoid it). Alternatively I could use Calcium Nitrate, but then I add to my GH which I also do not want. However, I recently switch over to DIY for Ca/Mg (using Calcium Chloride and Magnesium Sulfate) instead of Seachem Equilibrium. I wonder if I could switch out the Calcium Chloride with Calcium Nitrate? I am targeting a GH of 5-6 (my softened tap is “0” GH) for my WC water. If so, I will have to figure out how much Nitrate I will end up with if I would do that.

For phosphate it seems like there are two relevent options: Monopotassium phosphate and Dipotassium phosphate. The Dipotassium is supposedly more soluble. I guess it won't matter which I choose? As far as I can tell, I wont be able to avoid the K part of the Phosphate dosing anyway.

To simplify matters further, I am going to mix it all in with my weekly WC water with some basic trace as well, and probably skip my current mid-week dosing.

Cheers,
Michael
 
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X3NiTH

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To make it easy on yourself I would skip Calcium Nitrate and use Magnesium Nitrate instead (if using Magnesium Sulphate for dosing just reduce this dose to account for the extra dose of Magnesium from the Nitrate salt), the reason being that Calcium Nitrate has a tendency to be problematical with other salts and cause the formation of precipitates if you exceed the solubility rules for calcium if you try to make a concentrate (doesn’t have to be a solution CaNO3 will react with other dry salts if placed together in a sachet for easy dosing, been there done that).

It’s ok to dose CaNO3 it just doesn’t like being in a blend.

I wouldn’t worry about the K content from either of the Phosphates, use either (whichever is cheaper or easiest to obtain), it’s not going to really contribute much more to the new background level you have via water softening, you should be able to calculate the amount of K contributed by the water softener through either direct testing for K content post softener or calculating it via the reduction in hardness by comparing source hardness to softened hardness, background levels of K are usually around 2-3mg/L so your not likely going to have outrageous levels of K post softening.

:)
 

MichaelJ

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To make it easy on yourself I would skip Calcium Nitrate and use Magnesium Nitrate instead (if using Magnesium Sulphate for dosing just reduce this dose to account for the extra dose of Magnesium from the Nitrate salt),
@X3NiTH Thanks! That's what I am going to do then. Can you recommend a product? I did a quick search on amazon (US) and only a product that also contained magnesium oxide came up.

I wouldn’t worry about the K content from either of the Phosphates, use either (whichever is cheaper or easiest to obtain), it’s not going to really contribute much more to the new background level you have via water softening, you should be able to calculate the amount of K contributed by the water softener through either direct testing for K content post softener or calculating it via the reduction in hardness by comparing source hardness to softened hardness, background levels of K are usually around 2-3mg/L so your not likely going to have outrageous levels of K post softening.
In a previous discussion I calculated my potassium level in my WC water to be around 80 ppm - I am occasionally using more like 55-60% RO / 45-40% Tap so the number is probably more around 70 ppm.

Thanks for the feedback.
 
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X3NiTH

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If you are US based then a random search came up with these guys -


70+ppm of K shouldn’t be a problem, in the past I’ve run over 100ppm long term without issue.

:)
 

MichaelJ

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If you are US based then a random search came up with these guys -

Perfect! Thank you!

70+ppm of K shouldn’t be a problem, in the past I’ve run over 100ppm long term without issue.

:)
No, in isolation, I am not worried about the K levels at all - and haven't had any issues at all since switching over to Potassium salts in my water softener. I just want to keep my overall TDS in check for the sake of my recently introduced shrimps :) and I still suffer from a bit of TDS fixation from running my tanks (unknowingly) at astronomical TDS values. ;)

Cheers,
Michael
 

ceg4048

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I agree with X3NiTH. There is absolutely no mileage in worrying about using potassium salts for your nutrients. Any nutrients you dump into the tank when dosing EI will automatically raise the TDS, significantly. TDS as a number in isolation is not necessarily bad. What matters is the components that cause the TDS. The portion of the TDS due to water pollution is bad, but the portion due to nutrients is not bad. If you dose EI you should always do a large water change to reduce the pollution component of TDS. Heavily fed plants will produce lots of pollution and you will see the rapid TDS rise during the week specifically due to the organic waste being expelled by the plants.

You can easily determine what portion of the TDS is due to pollution. Measure TDS immediately after a massive water change. Then dose and take a TDS reading. This difference indicates the amount due to nutrients. You can then work out over the course of the week how much is due to nutrient dosing and how much is due to pollution.

One can always lower the dosing amounts as well. EI supply's more than enough nutrition so as long as the lighting load allows it's feasible to lower the dosing amounts.

Cheers,
 

MichaelJ

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Thanks, so I am getting this then: Magnesium nitrate and this: Monopotassium Phosphate. I am also looking at the trace mixes... I wonder if this trace element mix would work? It's so cheap compared to the "aquatic" formula's sold in cute bottles (mostly containing water.).

I guess I owe you guys a beer or something for all the money I will be saving :)

Cheers,
Michael
 
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MichaelJ

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That chelated trace mix looks ok!
@X3NiTH Just received the compounds mentioned above. Dosing the Magnesium Nitrate and Mono potassium Phosphate is pretty straight forward, but the question is how much I should dose the trace element mix to get a comparable amount to my current dosing of Tropica Premier (26 ml after weekly WC and 16-20 ml mid week) ? I suppose it would be way, way less! I never found a good reference to a "guaranteed analysis" of Tropica Premier or Tropica Specialized.

Also, I noticed that the mix is not containing Sulfur. Is that something I should be adding in addition? or is the background of my Tap/RO mix as I use Epsom Salt to raise GH to 5-6 (I will lower Magnesium Sulfate dose and add Magnesium Nitrate instead) enough?

Cheers,
Michael
 
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Wookii

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@MichaelJ the IFC Calculator is a great tool for working our dosing quantities: IFC Aquarium Fertilizer Calculator

If your trace/micro mixture is anything like the APFUK version, I would imagine it could be almost impossible to dose dry. If following an EI regime, you would be dosing around 0.12grams per 50 litres 3x per week. Making a liquid solution with a dosing bottle would be much easier.
 

Zeus.

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TPN gives [trace]at recommend dose
1625646698602.png

your CustomHydro trace @ 0.6grams per 100Litres yeilds ( edit as posted incorrect values 18/2/2021)
1629313933673.png

and for comparison with TNC trace and APFUK trace at same 0.6grams per 100L
1625646930507.png
 
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MichaelJ

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your CustomHydro trace @ 0.6grams per 100Litres yeilds
View attachment 171607
Hi @Zeuss Thanks a bunch for doing this! I think perhaps around 0.5g twice a week should be fine for my 151 Liter (40 US Gallon) heavily planted tanks. I will be a little low on Molybdenum though and a bit high on Copper contents, but I think my Shrimps should be ok with this. (I believe 1ppm of Cu is when it becomes a problem for dwarf shrimps).

@MichaelJ the IFC Calculator is a great tool for working our dosing quantities: IFC Aquarium Fertilizer Calculator
Hi @Wookii Unfortunately I don't have MS Excel and the IFC Aquarium Fertilizer Calculator won't work with the Numbers App on my Mac.
If your trace/micro mixture is anything like the APFUK version, I would imagine it could be almost impossible to dose dry. If following an EI regime, you would be dosing around 0.12grams per 50 litres 3x per week. Making a liquid solution with a dosing bottle would be much easier.
The Trace mix is already in liquid form fortunately, but to your point I will have to dilute it a lot anyway, like 32:1 to make it manageable for dosing. I suppose regular tap water will do as a mixer? I will use an empty Tropica 2ml/pump dispenser (1/32 mix) so that 8 pumps will give me the 0.5g per dosing (8 pumps x 2 ml * 1/32 x 1g) = 0.5g.


Cheers,
Michael
 
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Wookii

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The Trace mix is already in liquid form fortunately, but to your point I will have to dilute to a lot anyway, like 32:1 to make it manageable for dosing. I suppose regular tap water will do as a mixer? I will use an empty Tropica 2ml/pump dispenser (1/32 mix) so that 8 pumps will give me the 0.5g per dosing (8 pumps x 2 ml * 1/32 x 1g) = 0.5g.

Cheers,
Michael

Oh ok - I would use DI or RO water to ensure you don't get any reactions with anything in your tap water. You may also need to add some Potassium Sorbate to prevent any mould build up (depending on mow much you intend to mix up at once, and something to maintain the acidity of the mix to such as Ascorbic acid or vinegar.
 

MichaelJ

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Oh ok - I would use DI or RO water to ensure you don't get any reactions with anything in your tap water. You may also need to add some Potassium Sorbate to prevent any mould build up (depending on mow much you intend to mix up at once, and something to maintain the acidity of the mix to such as Ascorbic acid or vinegar.
@Wookii Ok, Thanks. I'll use RO water then. I will use an old Tropica 300 ml bottle, so a bottle would last 4.5 weeks, but I plan to make it part of the routine to mix a new every 4 weeks and just dump whatever is left. How much white vinegar should I add then?
 

Wookii

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@Wookii Ok, Thanks. I'll use RO water then. I will use an old Tropica 300 ml bottle, so a bottle would last 4.5 weeks, but I plan to make it part of the routine to mix a new every 4 weeks and just dump whatever is left. How much white vinegar should I add then?

Not sure on the vinegar, I use Ascorbic acid (vitamin C), but there is a thread here where @Happi adds 10ml per 400ml water to his custom micro mix:

 

MichaelJ

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Not sure on the vinegar, I use Ascorbic acid (vitamin C), but there is a thread here where @Happi adds 10ml per 400ml water to his custom micro mix:

Sounds good. Thanks! Given the short lifespan of a 300 ml bottle (4 weeks) I should be good with a similar amount (10ml) of vinegar.
 

Wookii

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Sounds good. Thanks! Given the short lifespan of a 300 ml bottle (4 weeks) I should be good with a similar amount (10ml) of vinegar.

The vinegar is just to acidify the mix to prevent the pH going too high and breaking the chelation of the micros. The Potassium Sorbate is for the longer term storage to prevent mould etc.
 

MichaelJ

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The vinegar is just to acidify the mix to prevent the pH going too high and breaking the chelation of the micros. The Potassium Sorbate is for the longer term storage to prevent mould etc.
@Wookii Thanks. Good to know. I will add 0.5g of Potassium Sorbate as well similar to what @Happi suggest for his custom mix.
 
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Happi

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If you are making a solution that is going to last for month or two, you can reduce the potassium sorbate to lower amount such as 0.25 gram per 500 ml solution.
 

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