Dosing of Potassium Sulphate - The Planted Tank Forum
 
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post #1 of 3 (permalink) Old 12-04-2009, 02:17 PM Thread Starter
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Dosing of Potassium Sulphate

Inorder to achieve 20-30ppm of potassium, I have added about 20g of potassium sulphate for my 100g tank. How long would that amount of potassium remain or consume by my plants if my tank is not heavily planted? Should I dose 20g on a weekly basis if I change 40% water weekly? Or I should only add 8g after I change water? Please advice.
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post #2 of 3 (permalink) Old 12-04-2009, 04:25 PM
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Those are good questions. There are a couple of "extreme" scenarios that might help us figuring out what to do.


Example 1

Assuming plants eat up all K. Your tap water contains no K, you don't dose anything else that contains K, you dose 20g which (after deduction of substrate, glass thickness, space on top = 80 gal) increases your K level to 30 ppm. Plants consume it, you do a 40% WC, and can dose 20 more grams.

Example 2

Assuming the K consumption by plants is negligible. Your water contains 7 ppm of K, and you dose 10g of KNO3 which adds ~13g of K. You add 20g of K2SO4. After a week went by, you do a 40% WC, and dose 20 more grams.


In example 1, at the beginning of the second week (second dosing) you are at 30 ppm again. In example 2, your tank would end up at around 75 ppm K after WC and dosing.

In my examples I mentioned some of the unknown variables. If we can't measure them, we can make assumptions. For example, how much of the K is being used by plants? It will be more than 0, and most likely less than the 30ppm that you are adding.

I like to err on the lower side of things. For example, I would assume nutrient uptake of plants would be zero. With a 40% water change, I would only add as much as necessary to bring the 40% up to the target level, so 20g * 0.4 = 8g. This will certainly assure that the tank doesn't run out of K, even though it might be a little less than your target level.

Simple thing I do: I have an EC meter, which measures electrical conductivity. The EC of my tap water is 0.60 mS, while I keep my tanks at ~ 0.95 mS. This doesn't exactly tell me the state of K, but it gives me an overall idea of the macro levels in my tanks. Other use different meters (TDS) or methods.

Sorry if that was too much.


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post #3 of 3 (permalink) Old 12-05-2009, 01:29 AM Thread Starter
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Hi Wasserpest
Really appreciate your advice. Think I'm gonna just add potassium equivilent for the amount water I change weekly.
Here are some information about my tank :
Dimension : 72 x 18 x 24 inch
Nett Volume : 403 litres / 106 gallon
Filtration : 1 x Eheim 2026 / 1 x Eheim 2260
Pressurized CO2 : current 15ppm (trying to achieve 30ppm)
Temperature : set 26'C
Lighting : 3 x 150W M.H (8 hrs daily)
Substrate : Vulcanit Fert + Lapis Sand

Flora
Phillipine Java Fern
Cryptocoryne Spirallis
Rotala Indica
Rotala Roundifolia
Rotala sp. Nanjenshan
Echinodorus "Red Diamond"
Blyxa Japonica
Limnophila Aromatica
Pogostemon Stellatus
Tonina sp. Belem
Nymphoides Aquatica
Nymphaea Lotus Zenkeri
Nymphaea sp. Rubra
Barclaya Longifolia
Aponogeton Ulvaceus
Eriocaulon sp.
US Fissiden Fontanus
Suessassertang
Spiky Moss
Intend to have Glossostigma as foreground carpet.

Fauna
50 Cardinal Tetras
5 Otocinclus (adding another 15 soon)
10 Tiger Shrimp (adding another 100 malayan shrimps)
3 SAE

Base on the above, would like to hear any advice on achieve better results in my tank. I also dose calcium nitrate & potassium weekly base on the amount of water I change. I have purchase WonderGro Macro + & Micro + but haven't dose them yet.
Yesterday night test :
PH = 7
KH = 5
CO2 = 15ppm
NO3 = 5ppm
PO4 = Nil

I'll try to post some picture later tonight when my children are asleep.

Cheers,
K.C
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