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Standard plant food

Do check what this fertilizer contains. A lot of these fertilizers use ammonium nitrate instead of potassium nitrate or another source of N ...
 
Well you really need to look at the fact that the product primarily derives it's Nitrogen from ammonia, so I'm fundamentally against products with such high Amoniacal-N. All it takes is one stupid blunder and the party's over for your fish/shrimp. This all depends on pH and temperature of course, and we really don't know the rate of NH3=>HN4+ equilibrium.

Also, it's complicated trying to figure out what the concentrations are. The straight ammoniacal-N value is easy enough. But the ammonia derived from urea has to be done stoichiometrically, because urea is converted by the enzyme urease in the aquarium sediment according to the equation:
(NH2)2CO + H2O ? CO2 + 2NH3
So, for every mole of urea, 2 moles of ammonia is generated.

Well, let's see what we can figure out...
50g of product evidently has 3.5% N-Ammonia
50g x 0.035 = 1.75g N-Ammonia
N is 82% by weight of NH3 so total ammonia from this source is 1.75g/0.82 = 2.13g NH3

In 500ml of water the concentration will be 2.13g x (1000) / 0.5L = 4260 mg/L
Each ml delivers 4.26mg NH3 per liter
Each 1/2 ml delivers 2.13mg NH3 per liter or 2.13ppm NH3
=============================================================================

50g of product reportedly contains 11.5% N from urea
50g x 0.115 = 5.75g N-Ureic
N is 47% by weight of (NH2)2CO so total urea from this source is 5.75/0.47 = 12.2g Urea

In 500ml of water the urea concentration will be 12.2g (1000) / 0.5L = 24,400 mg/L
Each ml will deliver 24.4mg urea per liter
Each 1/2 ml will deliver 12.2mg urea per liter
The molar weight of urea is 60,000 mg per mole
The number of moles per dose will be 12.2mg / 60,000 mg/mole = 0.000203 moles
Therefore:
0.000203 moles (NH2)2CO + 0.000203 moles H2O ? 0.000203 moles CO2 + 0.000406 moles NH3
Molar weight of NH3 is 17,000mg per mole
Weight of NH3 per liter produced by adding 1 dose of urea is 17,000 mg/mole x 0.000406 mole = 6.91mg NH3 per L

Total NH3 per dose = 2.13ppm + 6.91ppm = 9 ppm

I looked at the numbers, not very closely, but they look huge, so much so that I reckon I must have missed a decimal place somewhere. I'm sure I messed up somewhere.
On the face of it, it looks like you are adding a huge amount of ammonia to the tank. This is something like 100X above the lethal dosages for fauna. I assume that the NH4 equilibrium is achieved quickly so maybe this isn't a big deal. I just find this all very messy. For years folks have been winging about the evils of NO3, and here we have people happy to play with fire. Go figure... :crazy:

Cheers,
 
Thanks for the very comprehensive reply! Luckily I'm not using this in the Aquarium, just in pots on the window sill - see first post. I'll continue with it for now and use some Tetra PlantaMin when I fill the tank until I get round to buying some chemicals.

What do you think of the all-in-one recipe posted on the JPT site?
 
Well, I mean Tetra PlantaMin is on the other end of the spectrum. It's nontoxic, but it's also non-useful because it's just a weak trace only mix that costs 100X more than it needs to. Why wouldn't you just use the NPK dry powders that you can get from any of our sponsors? That makes much better economic sense to me. As I mentioned, all you have to do to adjust this Chempak product for use in a populated tank is to reduce the concentration by 50X to 100X, so that in a 500ml bottle, instead of dumping a tank busting 50g of powder in there you could just put 0.5 gram to 1 gram of the powder. That would render it much safer but you'd need to analyze the P and K components as well as the traces to see if it produces enough of those.

Sorry mate I have no idea what is JPT site. Got a link?

Cheers,
 
Oh yeah, of course. I've never seen it referred to as JPT. :crazy: Sure, this is well known. Lots of people use this and generally report success. The trick is that typically you're dumping this stuff into a tank that has a lowish pH so that helps to keep the Iron and the PO4 apart for a little while This mix depends on keeping the pH at around 6 to make the chelation work, so it's fine in the bottle but once in the tank the pH of the tank determines it's true effectiveness. In any case, all it has to do is to work for an hour or so because that's about as long as the the plant needs to uptake the Fe that it wants. And this is a lot cheaper than what Tropica can sell it for...

Cheers,
 
I'll try the JPT all-in-one recipe then. ;) I only mentioned Tetra PlantaMin as I've got some in the cupboard. :D
 
Hi all,
I've been away for a few days, but I think Clive is right about the nitrogen content, just using a "back of an envelope" calculation I come to 10ppm N, 12ppm NH3.

The fertiliser is 20% N, and you've used 100g in 1 litre (this just makes the calculation easier), so that is 20g total. You have then diluted this at 0.5ml in 1 litre which is 1:2000.

20/2000 = 0.01. So you have 0.01g of N. There are 1000mg in a gram and a 1,000,000 mg in 1litre/1 kg (water has a density of 1) so mg/l is equivalent to ppm.

We have 0.01 x 1000 = 10mg (or 10ppm N), all potentially as ammonia. 10ppm N is (17/14 * 10) ~ 12.1 ppm NH3.

I think the reason this isn't toxic as it appears it should is that the urea has to be converted to NH3 by microbial action (again as Clive says by microbes that contain the enzyme urease), so this will take a while to become available as NH3/NH4+.

Assuming we have some carbonates, a reasonable plant load and high levels of oxygenation that should ensure that levels of NH3 don't remain toxic, even at alkaline pH. To make maximum use of the ammonia assimilation, and dissolved oxygen production of the plants, I would tend to add any fertiliser towards the start of the photo-period, (when the lights have been on for an hour or so).

If you were adding this to tanks with livestock, I think you would probably have to go a lot more dilute, 10g in 500ml should be safe. Your fertiliser addition is then 2ppm N, 0.8ppm P, 1.6ppm K + traces.

cheers Darrel
 
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