Results of dosing potassium

[vinz]

Whole tank volume.

[talev]

Interesting topic. Here's a few more spanners off the top of my head.

Sulphates in the water can :

- be taken in by plants (even if grossly in excess) and stored as sulphate esters or inorganic sulphate.

- be metabolised and reduced by sulphate reducing bacteria within anoxic environments into the lovely h2s, which then reduces fe3 oxides and hydroxides in the substrate (laterite) to give mainly iron monosulphides which is that black precipitate in 'anaerobic' substrates.

- determine the PO4 concentration in the water. As long as the substrate contains oxidsed iron, PO4 will almost certainly be present because phosphate is almost always attached to Fe3 based minerals. As Fe3 oxides and hydroxides are reduced by h2s, PO4 is released as the Fe3 is reduced.

- act as a carrier anion for Al3 in the substrate and leaches the Al (which is toxic) out into the water column.

- lead to increased sulphur bacteria growths in waters having sulphate concentrations from 28mg/L to 190mg/L.

- be found typically in concentrations of 2mg/L to 30mg/L in rivers and lakes which do not have obvious sulphate inputs from runoff.

- be toxic to Fontinalis antipyretica above 100mg/L.

Chloride :

- is not dangerous by itself.

- will be harmful to freshwater organisms if it accumulates so much that it increases the salinity of the water significantly and affect normal osmosis.

[FC]

Dear Vinz,

You mentioned adding the dosage in term of "Whole tank volume".

How do you know that the plant consume all the dosage in a week?
If the plant doesn't, then is it true that the K2SO4 conentration will grow with the weekly full dose for whole tank volume?

Kindly advise.

Thanks.

[FC]

Hi Vinz,

I would appreciate if you were to advise me (see my above post questions).

Thanks.

Have fun.

[Nicky]

FC, I think if you do a search for either K2SO4 or PMDD you can find a discussion topic whereby some kind soul actually used a spreadsheet to do a calculation and find that if you do x% of water change every week and dose the same amount of K2SO4 after every water change, the volume of the chemical will stabilised.

I also asked the same question before.

[Allen_1971]

Agreed... but for the sake of simplicity, lets say we dose 20ppm of K each week, and only 5ppm is consumed at the end of each week... Also assume a 30% water change weekly

week1 start K = 20ppm     end=15ppm     water change = 10.5ppm
week2 start K = 30.5ppm   end=25.5ppm   water change = 17.85ppm
week3 start K = 37.85ppm  end=32.85ppm  water change = 22.995ppm

you can already see that the level begins to taper off... if you keep this up for 10 weeks you should basically see that your K level tapers off at about 54ppm at the start of the week 11

More importantly, the % of water change greatly affects this level... i.e. if you did a 20% and 40% water change respectively, you would find the K levels tapering off at 79ppm (20 weeks) and 42ppm (9 weeks)

[SuperRaY]

how about potassium hydroxide ? KOH? will it be safer than S, becoz o- h+ ions is present in pure water, does anyone have a insight on this ?

[Allen_1971]

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On 1/2/2003 12:33:24 PM

how about potassium hydroxide ? KOH? will it be safer than S, becoz o- h+ ions is present in pure water, does anyone have a insight on this ?
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Not too sure... returned my chemistry to my teacher years ago... but the question is do you have a ready source of Potassium hydroxide?

[talev]

how about potassium hydroxide ?

Potassium hydroxide is a very strong base which can cause blisters and serious skin burns upon mere contact. And any contact with water generates a lot of heat via a strong exothermic reaction.

Good in theory, but not so good in practice.

[Addie]

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On 1/2/2003 2:23:07 PM

Potassium hydroxide is a very strong base which can cause blisters and serious skin burns upon mere contact. And any contact with water generates a lot of heat via a strong exothermic reaction.

Good in theory, but not so good in practice.
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Agree! KOH is simply too alkaline to aquarium water. It will make your water pH goes way up!!

[FC]

Hi Allen,

Thanks for your reply.

"you can already see that the level begins to taper off... if you keep this up for 10 weeks you should basically see that your K level tapers off at about 54ppm at the start of the week 11"

I am puzzled???!!! now. I suppose that the target is to keep the K+ level for the whole water column at about 20-30ppm (just like keeping Fe at "n" level) at all time and not adding 20-30ppm of it weekly/at water change.

If your suggested method of dosing should be the way, then, the K+ & SO4 will keep growing non-stop with each water change. Am I right? I am confused now. At week 11, the SO4 will be approx. 70ppm and keep growing?!

Kindly advise.

Thank you.

[Allen_1971]

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On 1/2/2003 3:04:58 PM
If your suggested method of dosing should be the way, then, the K+ & SO4 will keep growing non-stop with each water change. Am I right? I am confused now. At week 11, the SO4 will be approx. 70ppm and keep growing?!
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FC,

I'm not suggesting that this is THE way to dose K, rather it is one of the ways that many of us use to dose K2SO4. The idea is not so much to try and maintain a fix level of K in our tanks. Although this would be more ideal, we are troubled by 2 problems. Firstly the inability to quantify how much K our plants is using. Secondly, the inability to check how much K is in our water.

Fortunately, we are fortunate that plants and fishes are both very tolerant of K, with people reporting levels as high as 120ppm being used. As for SO4, well that is more risky, using my above example... you are right to assume that the sulphate levels will rise to pretty high levels ard 70-80ppm. So far no one has had major problems reported yet.

If dosing K is really important, we can switch to using KNO3 or KCL as alternatives (to reduce sulphate levels).

[Allen_1971]

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On 1/2/2003 2:23:07 PM
Potassium hydroxide is a very strong base which can cause blisters and serious skin burns upon mere contact. And any contact with water generates a lot of heat via a strong exothermic reaction.
----------------

Talev,

Just curious, if we were to use potassium hydroxide, what would the likely chemical reaction result in? i.e. KOH +H2O = ?????

Also assuming that we wanna dose 20ppm K in a 100L tank, then we would roughly need 3 grams of KOH... given that the amount of KOH is so little compared to the volume of water, would the exothermic reaction cause problems? Off hand I'm doubtful...

[talev]

Potassium hydroxide will dissociate in water.

Simply KOH gives you K+ and OH.

But the story doesn't end here.

Then 2K + H(2)O gives you 2KOH + H(2). Yes you get KOH again but this time you have flammable H gas to deal with.

There is no need here to use Hess's law to determine the amount of heat produced in this exothermic reaction, but potassium usually gives enough heat to ignite the H gas to give a purple flame (More or less mass does not affect the temperature).

I was not concerned with any raises in overall tank temp, in case you were wondering. KOH is a recognised caustic irritant, and KOH and water combine to give so much fizzing, popping and smoking that it's hard not to get any on your skin or in your lungs. Imagine dressing up in lab suits just to prepare KOH.

And KOH is quite a dessicant to being with - open one bag or jar, close it, open it again in another week and there'll probably be a solidified crust on the top. Open it a few more times and you'll need an ice pick before you can use it.

But of course, I'm not saying no one can use KOH as a K source. I'm just pointing out some issues which people may like to know before they make their choices, especially since safety should be a prime concern.

[lip]

sorry to interrupt the interesting discussion, but i thought i could add a bit to results of adding potassium.

two weeks after i started a 20-25 ppm per week dosage (divided into 3 dosages over the week), photosynthesis of the plants definitely increased. tonight, i could observe quite a fair amount of plants bubbling, including the moss, stellata and hair grass. I am guessing that this is a direct result of the K dosage, since this tank has been set up for about 4 months now and I have never observed bubbling before.

Dosage of K does appear important to plants growth. i am using K2SO4. so i guess i am also anxious to know whether the S04 will affect the plant's and fish's health in the long term. unfortunately i can't contribute much on this at the moment. will post again if i find anything useful.

[hobbit6003]

Ok, it is nearly a month after dosing K2SO4. I'm adding approx. only about 5mg/L in total every week, and I'm seeing some results now.

Just before I started this regime of dosing K daily, my NO3 and PO4 reading is 20ppm and 1ppm (yes, after mths of neglect).

A week after I started my K dosing regime, I've managed to bring NO3 down to <5ppm and PO4 is unreadable. I even thought that something's wrong with my test kits that I went out to buy new ones!

As for algae reduction, I do see a significant decrease in the amount of new BBA forming, but the velvety hariy algae on the leaves remained, which I was reduced only after I bought some SAEs.

The rest of my water parameters are: pH 6.8-7.0, kH 4, Fe 0.25ppm, unreadable ammonia and NO2.

Inhabitants include a 40cm arowana, 20 panda corys, 15 mosquito fishes, 1 distichodus sexfaciatus, 5 ottocinclus, 5 small SAEs, 3 clown loaches, 2 juvenile bristlenose pleco, 1 yellow tiger pleco.

Cheers,

Kenny

[DEA]

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On 1/2/2003 9:58:04 PM

Potassium hydroxide will dissociate in water.

Simply KOH gives you K+ and OH.

But the story doesn't end here.

Then 2K + H(2)O gives you 2KOH + H(2). Yes you get KOH again but this time you have flammable H gas to deal with.

There is no need here to use Hess's law to determine the amount of heat produced in this exothermic reaction, but potassium usually gives enough heat to ignite the H gas to give a purple flame (More or less mass does not affect the temperature).

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pardon me but if i do say SO, the story stops when you get OH- and K+
the OH- might react with H3O+ in the water, but you will NEVER get elemental potassium from the abovementioned reaction

you will only get the flames if you use metallic sodium
metallium cesium gives an even more violent reaction
and you won't need to use hess's law to calculate as the values will have been long documented

[FC]

From Vinz,

"Within the first week of dosing K, my plants slowed down growing upwards. The stem between leaf nodes are shorter and stemmed plants grew bushier. Lower branches of Hygrophilia polysperma under bright lights dipped downwards, towards the substrate. I used to have to trim my Rotala indica once every week as they'll cover the 6 inches of space above quite fast. After my last trimming 2 weeks ago, they still have 1 or 2 inches of space to grow."


I noticed that my Rotala Macrandra and Ludwigia Brevipes have the same behaviour like yours. However, I am not sure if they are due to my K, NO3 or PO4 addition because I add them at the same time.
How do you confirm that it is K and not others?

I read an article about PO4. Lack of PO4 will turn plant reddy. It seems true to my Rotala Macrandra. Adding PO4 turns my Macrandra greener. I used to have them very very red.

Any comments?

[vinz]

Yes, it's a result of K dosing. Nothing else was new or changed. Results were similar for both tanks I tried it on.

You sure it's lack of PO4 causing redder plants? There's recent discussions at AquaBotanic about lack of NO3 resulting redder plants. Allen_1971 subsequently start a thread here about that.

[FC]

I cannot remember the site (will inform if I find it). It is about emerge plants and there are various defeciency symtom illustrated with photos.