Dry fertilizer dosing question. - The Planted Tank Forum
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post #1 of 6 (permalink) Old 04-19-2013, 07:19 PM Thread Starter
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Dry fertilizer dosing question.

I read barreport on using dry fertilizers such as KNO3, KH2PO4 and plantex CBM. i ordered them and wanna start dosing.

based on my 300gal water volume, im coming up with ~4.5 tsp KNO3, 1.5tsp on KH2PO4 and 1.5 tsp for CBM 3 times a week.

But this calculation is all based on 50% water change every week.

now what if i do less water change than this.
lets say 25% every week or 50% every 2 weeks or 75% once a month?

how does my dosing change?
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post #2 of 6 (permalink) Old 04-19-2013, 08:21 PM
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You can see how things will progress using this graphing site. It allows you to enter each dose as a ppm, percent of water changes, and frequency. I think the key to EI is to stick to a routine otherwise you'll end up needing to test levels and dose based on that.
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post #3 of 6 (permalink) Old 04-19-2013, 10:09 PM Thread Starter
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i saw the graph but how do i interpret this?
so whats my plan then?

nitrate target range is 5-30ppm
PO4: 1-2ppm
fe: 0.20-0.5ppm

i plan on 50% biweekly or 75% once a month.
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post #4 of 6 (permalink) Old 04-19-2013, 11:31 PM
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The ranges you have look good. A little tweaking is needed using the method below but it works. In the future you will need to adjust the dosing based on the uptake as well. In this example I am assuming a 25% uptake. FYI clicking the percentages in the legend will remove it from the graph making it easier to see.

Lets use NO3 as an example.

Using the nutrient calculator. Calculate how much KNO3 it will take to raise 300g of water to 30ppm.

The answer is 55.5g.

If we change 75% every month that will be 15 doses per month. So 55.5/15=3.7g

Using the calculator 3.7g will raise 300g of water to 2ppm

Entering that into the graph gives us a final range of 7.6ppm-24.4ppm using a 25% uptake. (You'll have to tweak the uptake over time)

Sound a little low? Add some to the graph to tweak it. Try 2.3ppm to the graph

Now we have 8.7ppm-28ppm.

So if we go with that value go back to the calculator.

To raise 300g of water to 2.3ppm we add 4.259g.

This is our final dose we add every other day.

Hope that makes sense.
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post #5 of 6 (permalink) Old 04-20-2013, 05:13 AM
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New tanks REQUIRE more care in the startup. ADA, myself, ADG, most experienced plant keepers suggest many water change sin the initial 1-2 months.

Eg, once every 3 days or so, 50% etc, then after. Typically 1-2 months.

By this time, you should know what good plant growth looks like.

Then slowly and progressively reduce the dosign till you hit a point where the growth and look of the plants is not the same/negative, then dose the prior highest amount.

NOW, you taper off the water changes.
Going once a week, then try once every 2 weeks, then once a month.

LESS light, lower temps and wise plant choices will make or break such lower frequency water change methods FYI.

More light, higher temps and stem weedy plants will make it much harder.
A 20-55 gallon tank that's a mess is not too bad to fix, a 300 gallon tank is a huge headache.

So while you decided/chose to have a larger tank, an ounce of prevention will be worth a pound of cure if you intend to avoid the work and simple management methods. So water changes are pretty easy compared to testing a lot, and dealing with algae and poor plant growth.
Most are not that lucky.

My advice is to make the water changes easier, send the waste water to yard landscape irrigation etc,

I automated several client's tanks in the 250-1600 Gallon ranges, they change about 10% daily automatically. So 30 gallons worth of water is pretty easy to deal with, changing your shower head can save this much.

Tom Barr
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post #6 of 6 (permalink) Old 04-21-2013, 07:35 AM Thread Starter
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Hey tom any good links on automated water change?
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