tsp doesn't just work for me.. i prefer grams..


Lifetime Members
Lifetime Member
Aug 6, 2008
Well, my first post here. First some background info:

I am from the netherlands running 6x54w T5 HO on my 130x60x60 cm tank. That is about 468liters (123 US Gallons). Since my water level is only 55cm high, and i have 5cm of filter sand on the bottom, i guess you could say that my water column height is 50cm. On the left and right i have 5cm of home-made background using styrofoam and epoxy, so that leaves 120cm in width. That background is also 5cm at the back of the tank, meaning i have effective tank dimensions of 120x50x55 equals 330 liters or 87 US gallons.

Next up, my sump: 100x50x40cm sump water level is approx. 30cm meaning that totals 150 liters or 40 US gallons.

Now, that means i fall into the category 100 - 125 gallon tanks since my water in my sump also needs to be fertilized.

100 - 125 Gallon Aquarium
+/- 1 1/2 tsp KN03 3x a week
+/- ½ tsp KH2P04 3x a week
+/- 1.25 tsp once a week(water change only)
+/- ½ tsp (30ml) Trace 3x a week
50% weekly water change

Basically my question is: How much grams is 1 tsp?

Furthermore, TPM is sold nowadays as "PLANT NUTRITION liquid" is that thesame stuff?

Tom Barr

Staff member
Jan 23, 2005
Teaspoon is a volume, not a weight, so different fertilizer salts will have slightly different weights.

Use the calculator above as a good tool to find what the average weights are for the various fertilizer salts.

Still, for maybe 15 Euros, you should be able to find a fairly accurate small weight scale to measure the weights of the fertilizers to get a close idea of precisely how much each level teaspoon might weigh.

That would be more accurate, but you really do not need such accuracy.
But the cost and effort is not much either for this.

Tom Barr


Lifetime Charter Member
Lifetime Member
Feb 14, 2006
Holland, Eindhoven
Hi Gilles,

For an accurate weighing scale, just check out a growshop (plenty of those overhere ;) )

I use an EI-(ish?) aproach with 50% waterchanges. The (mathematical) model behind it will give you that you'll get at most double the concentration of what you add in between 2 waterchanges. From this you can calculate back the amount of grams needed (together with your nutrient target ranges).

I myself am a bit messy and lazy, so messing around with different powders every other day doesn't attract me that much. So I make a stock solution which contains everything (one time messing around with powders ;) ). The stocksolution I made such that 10 ml doses exactly the amount I want (2mg/l NO3, 2mg/l K and 0.2 mg/l PO4; dosed every other day), and 10 ml I can obtain very fast using a suitable bottle (something like this).

So basically I add (a.o.) 1 mg/l nitrate a day. So suppose I definately don't want to have a concentration higher than say 28 mg nitrate/liter, I'll be fine (within the model) when I change water at least every 14 days.

(as you know I made a little calculator to calculate how to make the stocksolution given the netto volume of the aquarium. The dutch (beta) version can be found here. In case there is interest, I can of course make a translation)