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Potassium nitrate vs nitrogen

Kezzab

Member
Joined
18 Jan 2016
Messages
1,464
Location
Carlisle
Hi, I'm 100% not a chemist, so go easy.

There is a persistent cyano problem in my 220ish ltr sumped tank:
https://www.ukaps.org/forum/threads/stig-of-the-sump.48558/

It's not overwhelming but it's not nice. I want to address the root cause. Having read here that low nitrate can be an issue, i did a nitrate Test for the first time in forever. It indicated approx 10ppm.

The tank is well stocked, takes 5ml of EA complete plant flood and 4.5ml of TNC Carbon daily. (Carbon has only been being added for 2 weeks so far).

So, question:
- Would 10ppm be considered low? (I appreciate the debate about Test kit accuracy).
- If i wanted to increase nitrate levels would i add potassium nitrate or nitrogen (both available via TNC)? What's the difference?
- What would be a target level in the tank? 20ppm,50ppm, more?

Alternatively do i just increas my current fert dosing? (I think.this would be more expensive however).

I'm in the north west and tap water is very soft.

Thanks for the advice.
 

zozo

Member
Joined
16 Apr 2015
Messages
8,300
Location
Netherlands
It can take some time for a low tech to balance out especialy if a lot of wood is used in the hardscape.. In my case it took me over 6 months to ease it all down with extra water changes and gravel vacuming. I used over 5 kilo's of Mopani wood and the first 6 months it leached like hell the substrate was constantly covered with a light brown dust like fibre collecting in low flow area, diatomes, other filamentous algae and also cyano kept me bussy for over 6 months. I suspect it was from the wood, even it's dead it leached a sh|tload of organics into the water column disrupting the balance in rekation to current plant health and growth..I realy thought i created a monster beyond any help.. But in the end it all came together when plantmass increased and the tanke aged, it was my first time taking so darn long. So don't panic, just keep up the husbandry, do extra water changes and cleaning out algae as long as necessary.

I also started with complete fert mix from Tropica (special/green) it actualy didn't realy work out that well, i wasn't happy with the plant growth.. I changed to mixing my own with KNO3, KH2PO4, K2SO4, Epsom and Traces. Since i have > 20ppm N from the tap, i don't use much KNO3 if the plants don't say i should i don't add any at all. It also adds very little K, but that little K it adds also can't hurt it's neglectable. Anyway since i have rather high N and we definitively need K and P i weekly dose 20 ppm K and +/- 1,5 ppm P with adding 0.5 gram KH2PO4 and 6 gram K2SO4 on 100 litre tank.

Next to that i use floaters to tell me where i stand.. Search the forum and look up Darrels Duckweed index. You don't need to use Duckweed any other well growing floater will do, frogbit is a very valid candidate. Floaters get co2 from the atmosphere, so if these show any deficiencies it aint Co2 related, it must be fert or light related. If your floaters are happy than you have a happy water column regarding fert content, still problems with submersed growth, you have light. flow, temp or most likely co2 issues.

If 10ppm N is low is hard to say, it depends on plant stocking and light source.. But having 20ppm N also wont hurt and is about always enough. So i'm aiming towards a > 20 ppm N, 20ppm K and 1,5ppm P and add additional traces and magnesium. For a low tech this is at the high end values, i could do with less without the floaters, but it also doesn't have any negative effect on the submersed part. :)
 

dw1305

Expert
UKAPS Team
Joined
7 Apr 2008
Messages
13,844
Location
nr Bath
Hi all,
Because your water is very soft you could add some dGH, it might possibly be a lack of calcium (Ca) or magnesium (Mg) (if you aren't adding any?)
If i wanted to increase nitrate levels would i add potassium nitrate or nitrogen (both available via TNC)? What's the difference?
You can't add nitrogen on its own, the N2 (nitrogen gas molecule) is inert (it is ~78% of the atmosphere we breathe) because the two nitrogen atoms are very tightly bound with a triple bond.
main-qimg-7483b7da3316989b7b9ba31db47f41ab-c

If you can break that triple bond, the nitrogen atom is highly reactive and will form all sorts of compounds (<"fixed nitrogen">), including nitrate NO3, with the equally reactive oxygen (the triple bond is why you have three oxygen atoms in NO3).

Because NO3 has three oxygen atoms you need to use a conversion factor to go from mg L-1 (ppm) N to ppm NO3 (and vice versa). The RMM of NO3 is 14 (RAM N) +(3*16 (RAM O)) = 62 and the %N 14/62 = 22.6%.

To convert nitrate-NO3 (mg L-1) to nitrogen (N) (mg L-1): N (mg L-1) = 0.2259 x nitrate-NO3 (mg L-1)
and
to convert N (mg L-1) to Nitrate-NO3 (mg L-1): Nitrate-NO3 (mg L-1) = 4.4268 x N (mg L-1).

Potassium nitrate (KNO3) is highly soluble, so when you add it to water you get NO3- and K+ ions. To work out the proportion of both it is back to the RMM. The RAM of potassium is 39, so you have 39 + 14 + (3*16) = 101 and ~14% N, ~ 62% NO3 and 39% K.
But having 20ppm N also wont hurt and is about always enough
Should be about right.

cheers Darrel
 

ceg4048

Expert/Global Moderator
UKAPS Team
Joined
11 Jul 2007
Messages
9,598
Location
Chicago, USA
Just add more KNO3 and get on with it.

Add about 1/8 teaspoon per 20 USG weekly or bi-weekly. So for 60 USG add between a quarter to half teaspoon.

Stop testing for NO3 because those time wasting kits cannot tell you anything.

Dirty filters can also trigger BGA.

Cheers,
 

rebel

Member
Joined
4 Aug 2015
Messages
2,265
Sounds like a nice tank. Any pics?

My view of BGA is just a distant memory. I usually dose chemiclean once and it never comes back for the life of that tank.
 

rebel

Member
Joined
4 Aug 2015
Messages
2,265
I can see some GSA and maybe GDA/green fuzz. Are you sure it's BGA?

One interesting trial would be to dose some excel for two weeks and observe.

Whatever you do, if you are keen to find answers to the problem, do one change at a time. However, don't be surprised if you don't necessarily find a definite cause.
 
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