# Planted Tanks > Fertilisation and Algae >  PMDD ~ Whats the function of SO4 in a planted tank.

## smgwee

Having to achieve 20ppm of K &amp; 5ppm of mg, the combine SO4 will be > 30ppm (from K2SO4 and MgSO4). 

Will the level of SO4 cause any problem to the plant tank? Whats the role of SO4 in a planted tank? Is it redundant?

Side notes:
I had taken account of minimal K obtained from KNO3 (&lt;3ppm) and KH2PO4 (&lt;0.5ppm).

Regards
Gwee Sia Meng

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## bclee

Sulphur is one of the macro nutrients required by plants.

Sulphate is involved in protein synthesis and is part of the amino acids, cystine and thiamine, which are the building blocks of proteins. It is an essential nutrients for the plants.

There is not much report (if any) of sulphate toxicity in aquariums.

BC

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## smgwee

Thank BC, but >30ppm of SO4 seems high....

regards
Gwee Sia Meng

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## PeterGwee

Sia Meng, which is why large water changes are recommended when you go about such dosing regimes. Levels do not buildup too high if you keep up on the water changes.

Regards
Peter Gwee  :Wink:

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## smgwee

Thanks Peter, so it is not really a problem dosing 30ppm of SO4 into our tank. 

Anyway,I had been using PMDD for quite sometime now and I found it rather troublesome as I keep 5 bottles of stock solutions. I am thinking of mixing all the compounds together. I wonder if there will be any chemical reactions between the 5 compounds?

They are mainly KNO3, K2SO4, MgSO4, KH2PO4, Rexolin APN (Micronutrient Mix).

My formula is

1 teaspoon of KNO3
6 teaspoon of K2SO4
6 teaspoon of MgSO4
0.25 teaspoon of KH2PO4
1 teaspoon of Rexolin APN (Micronutrient Mix)

The above will be mixed with 300ml of H20, thus 15ml of this stock solution to a 50 liter tank will give me:-

NO3~~3.45ppm (Target 5ppm)
K from KNO3,K2SO4,KH2PO4~~ 18.60ppm (Target 20ppm)
Mg ~~3.15ppm (Target 5ppm)
PO4~~0.90ppm (Target 1)
Fe~~0.29ppm (Target 0.25~0.5ppm)

I am very happy with the calculation, however I wonder if the mixing will cause any chemical reactions.

Regards,
Gwee Sia Meng

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## PeterGwee

Sia Meng, you do not need the additional K from K2SO4 if you dose enough KNO3. The K from the KNO3 is more than enough as folks have found out. It does not harm though but its a waste. Just note that if you are having a high light tank, it does not pay off to dose leaner as you are setting up a crash prone scenario (uptake varies a great deal depending on plant mass and many other factors. As long as the nutrients do not run out, plants generally have no issues. A leaner dosing rate ups the potential of bottoming out the nutrients if you fail to keep the plant mass in check and let it overgrown and etc.). A lower light tank with NO FL of 1.5W-2W per gallon would be a better choice if you go the leaner way.

Regards
Peter Gwee  :Wink:

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## smgwee

> you do not need the additional K from K2SO4 if you dose enough KNO3. The K from the KNO3 is more than enough as folks have found out


Hi Peter,

Thanks again for your prompt reply. I am actually quite puzzled. The usage of KNO3 is usually targeted at the NO3 and it is recommended not to exceed 5ppm (Correct me if I am wrong). At this rate, the K is merely less than 4ppm as compared to the recommended concentration of K in a planted tank. (Usually 20ppm~30ppm)




> Just note that if you are having a high...... a better choice if you go the leaner way.


Points noted, Thanks!

Anyway, can anyone answer this question. 


> I wonder if there will be any chemical reactions between the 5 compounds?


Thanks!

Regards,
Gwee Sia Meng

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## dts_spawn

i don't think it will be a problem as even if they react, they will only be changing 'partner', E.G. 2KNO3 + MgSO4 ---> K2SO4 + Mg(NO3)2
so the ions will still be there for the plants. But there are some concerns. the reaction might be exothermic or the compound formed is not soluble. but from the compound you have, i don't think that there will be any problem. BUT just test 1st just in case.  :Smug:

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## Heuer

There should not be any chemical reaction by mixing the different compounds together. I have been doing this for about a year by mixing KNO3, KH2PO4, TMG into a 1.5L bottom and just shake well with tap water and pour them into to tank. Every is ok till today.

Too much trouble doing one by one!  :Grin:

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## GaspingGurami

[quote:163c82ab8f="smgwee"]Thanks again for your prompt reply. I am actually quite puzzled. The usage of KNO3 is usually targeted at the NO3 and it is recommended not to exceed 5ppm (Correct me if I am wrong). At this rate, the K is merely less than 4ppm as compared to the recommended concentration of K in a planted tank. (Usually 20ppm~30ppm)
[/quote:163c82ab8f]

Sia Meng, too much potassium can block uptake of magnesium and calcium. I used to dose K carelessly, thinking that it is one of those "won't cause trouble" ferts. Wrong.

One day, the new leaves of my Echinodorus oriental (which normally grows as hot pink) came out pale. I suspected Iron deficiency so I whack in the Fe. No use. Leaf turned paler as the days go by, and deformed. Aha, calcium deficiency. But how can? I have 5dGH in my water...

Stopped the K2SO4, and the hot pink returned to the new leaves. Too much K.

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## PeterGwee

[quote:b15f06d3b9="GaspingGurami"]Sia Meng, too much potassium can block uptake of magnesium and calcium. I used to dose K carelessly, thinking that it is one of those "won't cause trouble" ferts. Wrong. 

One day, the new leaves of my Echinodorus oriental (which normally grows as hot pink) came out pale. I suspected Iron deficiency so I whack in the Fe. No use. Leaf turned paler as the days go by, and deformed. Aha, calcium deficiency. But how can? I have 5dGH in my water... 

Stopped the K2SO4, and the hot pink returned to the new leaves. Too much K.[/quote:b15f06d3b9]

High K blocking uptake of Ca and Mg is not true as some folks including Tom Barr and Erik has proven. If somebody manages without issues with high K, you need to rethink your assumptions. Have you check your CO2? Is it consistent? NO3? Are you measuring it with some crap kit? Check and recheck CO2 and in doubt, add more. The rest can be said for the nutrients as well. Add more or increase the frequency of dosing to make sure that things don't run out. Give it a run for 3-4 weeks and make sure you keep up on the CO2. The dosing should be pretty consistent.

Regards
Peter Gwee  :Wink:

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## GaspingGurami

[quote:7bae781cfd="PeterGwee"]High K blocking uptake of Ca and Mg is not true as some folks including Tom Barr and Erik has proven. If somebody manages without issues with high K, you need to rethink your assumptions. Have you check your CO2? Is it consistent? NO3? Are you measuring it with some crap kit? Check and recheck CO2 and in doubt, add more. The rest can be said for the nutrients as well. Add more or increase the frequency of dosing to make sure that things don't run out. Give it a run for 3-4 weeks and make sure you keep up on the CO2. The dosing should be pretty consistent.

Regards
Peter Gwee  :Wink: [/quote:7bae781cfd]

Haha. I have a small tank (20L) and it is very easy to overdose. I used to dose dry measure and OD'ed 600ppm of KH2PO4. Now I keep bottles of mixed concentrate, but still easy to get carried away and OD.  :Wink:  

Sometime last month, I wrote: 



> Posted: Fri, 16 Jul 2004, 14:37 Post subject: Re: What is nutrient imbalance? 
> GaspingGurami wrote:
> 
> Hypothetically, can't I just dump in say 15 watts per gallon of lights, 60ppm of CO2, 60ppm NO3, 24ppm PO4, 60ppm K, 1ppm Fe (and whatever trace that comes with the LGA), then sit back for a week till water changing time before feeding again? There should be plenty of nutrients to prevent anything from running out for the week. Er... maybe the Fe will, which I'm willing to drop in daily, but the rest should have plenty to spare what.
> 
> 
> That's a huge amount of dosing. You are serious? 
> 
> More doesn't mean better. Having nutrients in excess definitely cause more harm than good. It may block other nutrients from being taken up. Eg. see this discussion 
> ...


I was in the "curious" state of mind at that time of writing, and wanted to know if I keep pumping in all the necessary lights, CO2 and nutrients, I could get the plants to take them all in and grow faster, pearl more, etc. 

Below was my water parameters at the end of 1 week's wild abuse. I used Sera testkit for NO3 and Fe, Red Sea for PO4 and AP for kH, gH. I had to dilute the watersample with distilled water in order to test for NO3 and PO4:

Volume: 20Litres
Lighting: 36 watts x2 PL, 6500K, 10mm from water surface
Temp: > 32degrees, thermometer ends there
CO2: Tank, 170ppm
kH: 18dkH gH was not tested, but at last water change a week ago, was 5dgH, from some coral chips.
pH: 6.5 before lights out, 6 before lights on
NO3: 240ppm daily dosing of 30ppm KNO3
PO4: 24ppm Daily dosing of 2ppm KH2PO4
Fe: >2ppm beyond my colour scale, the test solution became deep purple
K: dosed 60ppm from K2SO4 daily
50 drops of LGA daily

Observations:
Evaporation was around 1.5 litres per 24 hours
No filter was used, only a 200LPH powerhead to move water around
No fishes involved in the test  :Wink: 
Plants did not pearl after the second night, green hair algae and bba grew. E. oriental started to wither at the leaf edges and tips, and new leaves were pale and later deformed. Vals melting from the tips down. Riccia are dark green and sinks to the bottom, Banana plant shed all its submerged leaves and put out a lot of floating leaves. Evaporated water leave white salt deposits on these leaves. E. tennelus leaves start to brown. Marimo ball turned brown and melted from inside out. Cabomba that was trimmed down to the roots (thought I would have killed them by doing that) put out new shoots  :Crying:  

At the end of the week, I trimmed as much as I can, drained water to the gravel while vacuuming, topped up with fresh water, drain all again, topped back to the correct level, raised the lamps on their 3-inch stands, added 5ppm NO3 from KNO3, 0.5ppm PO4 from KH2PO4, 20 drops of LGA, a squirt of anti-chlorine, 1 flat 5ml tsp of baking soda (5dkh), bubbled CO2 till pH 6.8 then adjust back to 1BPS, turned on the lights and in 2 hours, the plants bubbled! 2 days later, the colour of new growth on the oriental returned to hot pink, although those that grew white stayed white  :Sad:  

I think this will be my last crazy excursion that I'll undertake for a while.

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## GaspingGurami

Re read the thread again and realised my last posting is totally off topic.  :Opps:  

Sorry.

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## Plantbrain

If you add most types of GH builder, at least one of them is SO4 based.

If you add MgSO4 * 7H2O, then you have plenty of SO4.

SO4 and Ca can be quite high and have no effect at rather high levels.

Ca/Mg blocking K+ etc, this occurs at VERY high concentration is soil pore water and they also act as a second messager in some stomatal functions and folks have confused something off the wqeb without understanding it. 
Then someone else jumped in and then another, but if you look at it critically, this does not occur even at 50-100ppm of K+ and Ca levels at 100pm or less, roughly a 1:1 ratio.

Regards, 
Tom Barr

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## smgwee

Thanks guys!!

As earlier mentioned, my actual concerns were:-

No. 1
_High SO4 level as a result from K2SO4 and MgSO4._
Peter and Tom had address this issue. Thanks!

No. 2
_Chemical reactions from mixing the various compounds in preparing stock solution to be stored over a period of time. (perhaps 2 months per mix)_

Heuer, you mentioned that you had been doing that, I will appreciate if you can elaborate further. Is you stock solution prepared for immediate or rather single dosing? Or for future use? I intended for the later.

Willy thanks! Any other opinions? Anyone??

regards
Gwee Sia Meng

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## Heuer

I don't stock them. Whenever i need to add these compounds, I just put the right amount all into a 1.5L bottle and add tap water together with a good shake. This should not take more then 1 min.

If you just want to add K, I suggest u stock as it take quite a large amount of water to disolve the powder.

Cheers!  :Smile:

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## smgwee

[quote:49edf3a45b="Heuer"]I don't stock them. Whenever i need to add these compounds, I just put the right amount all into a 1.5L bottle and add tap water together with a good shake. This should take more then 1 min.[/quote:49edf3a45b]
Thanks Heuer. All my planted tanks are less than 100 liters, so I will prefer to stock them for convenience. Thanks again for your info.





> If you just want to add K, I suggest u stock as it take quite a large amount of water to disolve the powder.


I am aware that K2SO4 has low solubility.. about 10~12g per 100ml.

Regards,
Gwee Sia Meng

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## Anubias

If one has fish in the tank, one must add at least some K2SO4 to balance out the nitrates that they produce. Some potassium sulfate is always necessary in a planted tank if the tap water contains 1 ppm potassium or less. I add about twice as much K2SO4 as KNO3. I also assume, rightly or wrongly, that the plants uptake a bit more potassium than nitrogen.

Regards,

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## Plantbrain

No, K2SO4 is not needed unless you have roughly 70-75% of your Nitrogen supply coming from fish waste(assuming no K+ supply from fish food/waste).

The amount used by plants is about 4 N's per 1K+'s for KNO3 dosing.

If you have a high NO3 in the tap water or a higher fish load, then K2SO4 is useful.

You can see for yourself if you do not have high fish loads/feedings.

Use KNO3 only. It should do the same thing.

Adding K2SO4 will not hurt either........
Some suggested that it would, I did not find it to be valid when I performed the test. I also had a long time experience using K2SO4 at excessive levels.

Regards, 
Tom Barr

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## Anubias

Hi Tom,

My guess that the K requirement would be greater than that for N was based on some dry weight analysis of aquatic plant material that George Booth or someone had placed on the aquaticplants list. Since fishfood doesn't have too much K, I've always added K2SO4 as well as KNO3. Tom, are you sure of the K to N ratio? It doesn't seem correct to me.

By the way, recently my plants are doing better since I upped the CO2 injection and added phosphate and extra nitrate. Also the lighting was decreased by 33%. I still use DIY CO2 on a 180 gallon, but pearling does occur.

In any case, your method of overdosing with key nutrients and doing weekly water changes is an award winner. For years I couldn't figure out why my plants grew o.k., but many looked so decrepit. I tried everything from manganese chelate to boron -to no avail. The CO2 injection must have been insufficient for the 750 watts. I should have tossed all of the test kits and bought myself proper equipment to titrate for CO2 using Na2CO3.

Too bad I didn't consider your advice sooner.

As an aside, I've never figured out how Nature is able to provide 10 ppm of CO2 to the tropical stream through the simple decay of leaves and debris and not have the CO2 outgassed. That's a lot of decay.

Regards,

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## Plantbrain

It's correct, I used Epstein's(1972) dry weight for my reference.

I double and triple checked my ratios required for roughly the 4 times referenced amount of N vs K. 

This also assumes *no*  K comes from fish waste/food.

The simple test is does it work or not, addig K2SO4 will not hurt, so you can add that if you wish still, but adding it will not help unless you have a large fish load/less light etc, George Booth did/does, Discus in a lower light CO2 enriched tank. So he likely has a need for K2SO4.

I tend to have low fish loads, sometimes none at all, to see what specific nutrient issues arise.

But some references to my ratio and usage of KNO3 as the sole source can be found on the APD and also Aquaria central's plant forum here:
http://www.aquariacentral.com/forums...ad.php?t=21033

So if you want to check the math and chem, be my guest. 

Regards, 
Tom Barr

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## hobbit6003

Guys,

Salts do not react with one another.

Cheers,

Kenny

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## Anubias

My understanding is that the ratio of 1.5:1 is a ratio of nitrogen to potassium by weight. In this case if half of the nitrogen comes from fish food and decay and half comes from the addition of KNO3, then there is available twice as much potassium as one needs. I guess that it all started with the introduction of the Sears and Conlin PMDD formula.

Assuming neither potassium nor nitrogen in the water supply, solving for X in the formula 61X2-178X+89=0, where X equals the maximum percentage of nitrate produced by organic processes and where 1-X is the percentage of nitrate to be contributed by adding KNO3, yields a situation where K and N are balanced. This point is near where approximately 64% of the nitrate is coming from decay and 36% from KNO3 addition. Beyond this point, one must add potassium in a form other than KNO3.

One of you science guys can check this out as I have grade ten chemistry and not much more math.

Regards,

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## Plantbrain

Make sure you use elemental N and not NO3 and P and not PO4 etc when you do the weights.


Regards, 
Tom Barr

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