Dossing EI Dry, Does lighting intensity affect standard dosage?


Junior Poster
Apr 11, 2010
New to dry ferts still, im using as a guide. Im trying to write up a dose for my tank.

135 Litres / 35 Gallons / 4wpg T5 7hrs 3pm-10pm / Co2 40ppm+

Does higher lighting intensity have affect on the dosage? should I bump up to the 150-225litre dosage? or do i wait for the next water change and take results from a nitrate test kit and adjust?

Also does macro run out first in the water column before traces?

80-150 litres
1/4 tsp KNO3
1/16 tsp KH2PO4
1/16 tsp traces

150-225 litres
1/2 tsp KNO3
1/8 tsp KH2PO4
1/8 tsp traces


Plant Guru Team
Lifetime Member
Jul 6, 2009
The Netherlands
Since the dosage is for 2 to 3 WPG, and you're using 4 WPG, I'd step up on the ferts to the next level and be sure that no limitation occurs.

You should think about using only 50% of the light you have now. That way everything is more managable. CO2 and nutrition demands are easier to meet. My old tank was a 55 gallon with 70 Watts of T5. I could grow every plant I wanted. if you go down to 50%, which is 2 WPG, you still have plenty of light.

What runs out first? Mostly NO3, but you should make sure nothing runs out.....ever.



Lifetime Charter Member
Lifetime Member
Jan 15, 2009
As Dutchy says, light drives it. I would add that what depletes your nutrients are the plants. If you have fewer plants you won't need as many ferts. That said, at the light you're running, fewer plants = more algae. So it's related, just not quite as directly. Lower light will require fewer ferts and you can get away with less biomass if that's your desire ( or you haven't yet gotten enough due to $$$ or whatever ). Higher light will definitely need more plants to keep the algae in check and you'll need plenty of nutrients to keep them growing.

Do note that at your lighting levels, CO2 is a nutrient you also need to keep on top of.

If you're dosing EI then none of your nutrients, micro/macro should run out at all. If you dose as recommended, then you put in enough macros for a little bit more than two days growth. By the time it's getting to the point where you might not have enough for good plant growth, you dose again ( every other day ). By the end of the week, you should have a little bit of extra left over which the Water Change takes care of. The same applies for traces. The difference is that with the traces, being well - trace amounts, the Water Change should provide enough of them for the first day or so, then you add more.

You could think of it as two cups, one for macros and one for traces. Each cup has a line on it. Below that line is poor plant growth. Each cup has a small hole in it which represents what the plants use and it will always be draining. Your job with EI is every other day ( adjustable ) you add enough ferts to the cup to make sure that at all times you have at least enough to be above the line. In most cases you won't be dumping in enough to be a problem, but you want to make sure you're always above that line and it's easier to be above that line by a bit if you add a little too much so there's still extra by the time you come back in a couple of days to add more ( dose ) the cup. At the Water Change you effectively empty the cups and add more ferts.

Maybe that analogy helps, hopefully it's clear enough and not confusing.

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Lifetime Charter Member
Lifetime Member
Jan 5, 2009
Washington, DC
Yes, sort of, not really.

Hi Vinno,
Lighting effects a lot of the things your working with. The type of plants we grow and how many we have effect nutrient uptake. Limiting nutrients (CO2 in a nutrient) can effect growth and nutrient uptake as well. The EI doses are based on the nutrients used by plants under high light (like yours) and CO2 rich tanks. Hmmm, also like yours. Primarily, lighting effects the demand for CO2. With sufficient CO2, plants need more nutrients to keep up with growth.

Dutchy has a good point. Your light fixture could drop to 2wpg. Most people are able to grow any plant with 1.7wpg, 30ppm of CO2 and EI doses. I use a full EI dosing with 1.2wpg and plants like Echinodorus, Vallisneria and dwarf hairgrass. If you have a good number of hungry plants, the doses for a 150-225 liter water column would be a safe place to start with 4wpg and 40ppm CO2. If you have a lot of fish, feed them heavily, decide to reduce your light to 2wpg and have a sparsely planted tank then watch the plants while you drop down the dose every two weeks. You might try and go a little leaner. There is no real harm in dosing higher. There is only so much a plant needs in a day, even with 4 wpg and CO2.

Here is some reading if you haven't already come across it that might be helpful.