Potassium Source and Amount - The Planted Tank Forum
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post #1 of 5 (permalink) Old 12-21-2015, 02:07 AM Thread Starter
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Potassium Source and Amount

Greetings Fish & Plant Wizards!

This is my first post so I apologize if I miss something or am unclear. I've been reading stickys and other posts for a few weeks and I'm one week into a new fertilizer plan so I think it's time to get some advise.

I converted my tank over to live plants over the last several weeks and I'm at the point where I would like to dial in my fertilizer dosing, and I have a couple questions:
  1. Since there are fish in there, do I really need to add nitrates / KNO3?
  2. Does the natural bacteria cycle create KNO3, or is it another type of nitrate that doesn't have potassium?
  3. Why doesn't the pH test strips show the same value as the meter during the day while I'm injecting CO2?
  4. Do I need to run a bubbler at night?

My Tank Parameters are as follows:
  • Lighting: I have a Kessil 360 Tuna Sun for general growth, and a Current USA Orbit Marine to make the glow fish pop at dusk and for some general growth as well. Currently, the lights run for 12 hours, from 8 am to 8 pm. I had them on longer but started to get some algae so I cut it back.
  • Size: 45 gallons
  • CO2: The normal pH of my water is around 7.8 and I'm regulating it down to about 6.5 while the lights are on, the C02 starts at 5 am.
  • Water flow: There is plenty of water flow. A small power head moves the water around randomly throughout the day.
  • Temp: 77 degrees F
  • Air: There is no bubbler.
  • Hardness: The GH runs from 150 to 300 from what I can tell from the strips.
  • Alkalinity: The KH runs from 120 to 220, again from what I can tell from the strips.
  • Tap Water: The tap water is reported to have a Ca level of 38 ppm and Mg level of 12 ppm according to the Jardine plant measurements here: http://www.dpwc.org/wp-content/uploa...5/05/cca14.pdf

I mixed up a dry batch of fertilizer from Greenleaf Aquariums. I followed their recommended feeding of 1 ml / 10 gal for the first week of the following PPS Pro ingredients mixed with 500 ml of water (and micros too - plantex CSM+B):
  • KNO3 - 33g
  • KH2PO4 - 3g
  • K2SO4 - 29g
  • MgSO4 - 20g

More questions:
  1. I was thinking of mixing up a batch without the MgSO4 and KNO3 and using that instead, or to replace a couple days, would that be OK?
  2. Would it be OK to dose 3 days worth of fertilizer every 3 days instead of one day worth each day?

Thanks for reading, and happy hobbying to everyone!


p.s. Here are the plants I have in there now:
  • Palustris Proserpinaca
  • Anubias bateri Nana
  • Montecarlo Micranthemum
  • Siamensis Hygrophila
  • Rubin Echinodorus
  • Aponogeton longiplumulosus
  • Ceratopteris thalictroides
  • Cabomba Caroliniana
  • Eleocharis acicularis
  • Cryptocoryne Parva
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post #2 of 5 (permalink) Old 12-21-2015, 02:46 AM
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The goal of PPS is to dose just what the plants will use, no more. It is considered to be better to dose slightly less than the plants would use to avoid dosing more than they will use. If that appeals to you you need to dose daily, not every 3 days. When you dose every 3 days you have to have more fertilizers in the water than the plants can use for at least 2 of the 3 days.

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post #3 of 5 (permalink) Old 12-21-2015, 03:10 AM
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Fish food contains most of the elements that plants need, but not always in the right ratios.
Fish food is low in potassium, iron, calcium and magnesium.
The proteins in fish food get digested by fish, and decomposed by microorganisms and enter the water as (among other things) ammonia (NH3) and ammonium (NH4).
Different organisms remove ammonia and return nitrite (NO2) to the water.
Different organisms remove nitrite and return nitrate (NO3) to the water. This nitrate is not combined with anything else.

Plants can use all these nitrogen containing molecules.
Fast growing plants can use up all these and need more.
The NO3 test is a good way to tell if the plants are using all the nitrogen from fish food, and if they need more.

One common way nitrogen is added to the tanks is in the form of KNO3.
This supplies potassium (which fish food is low in) and nitrogen.
If your NO3 test shows that the plants are not even using all the NO3 from the fish food your plants would still need a supplement that provides some potassium.
K2SO4 is a common fertilizer that supplies potassium without the nitrogen.

Fish food is low in calcium and magnesium. If the water you are using for the tank has a GH of at least 3 German degrees of hardness, then there is probably enough Ca and Mg. If you think there is a problem, then dose a GH booster that contains both Ca and Mg. Do not dose JUST Mg (Epsom salt or other) unless you have figured out that the water has enough Ca, and is only lacking Mg.

Fish food is low in iron. A chelated iron will remain available to the plants for the longest time. Simpler forms of iron get locked up pretty fast, so are less useful in the tank.
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post #4 of 5 (permalink) Old 12-21-2015, 11:47 AM Thread Starter
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Thanks guys!

It sounds like I need to keep on my NO3 testing to see where I'm at. The strips are telling me it's somewhere around the 20 mark, and it's pretty consistent; however, sometimes it dips down to the 10 mark. How much do the plants need?

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post #5 of 5 (permalink) Old 12-23-2015, 04:11 AM
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10 to 20 is a good reading on NO3. If your reading a 0 on NO3 then the plants are consuming everything which leads to a lack of nutrients

75 Gal High Tech Planted tank, 37 gal Low Tech
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