How much KNO3 to use?

[foocp]

Just bought KNO3 from HPC. Tried to create a concentrated solution to add to my 2ft tank by following the calculation given at Chuck's Website but I know that the KNO3 contents is different between Chuck's and HPC. I tried 1 to 7 tablespoon to 280ml of water and add some of the solution to my 2ft tank, but my Sera NO3 test kit keeps telling me that my tank has 0ppm NO3 even after adding KNO3.

So I decided to test perform the following test:
1. Take tap water and test NO3. Result = 0ppm
2. Take one tablespoon and mix with 20ml of water and test NO3. Result = 5ppm.

So my question is:
1. Test kit is not reliable (Thinking of getting another to compare result)
2. Need to add plenty of KNO3 to bring my 2ft tank to 5ppm?

Just to find out how much KNO3 do you guys use to make a concentrated solution?

Thanks!

[PeterGwee]

Am I right to say that you use 1 tsp of KNO3 to 20ml of water for testing? That would give you a super red sample as the test result as the amount of NO3 is simply too concentrated!!! Your test kit is junk, expired or you did not do the test properly. Most of the time, this kind of hobbyist kit are not cut out for such purpose. I have tried them and they have given me erratic results.

[Plantbrain]

Add roughly 1/4 teaspoon for about 10ppm for an 80 liter 2ft tank.

This will need to be added 2-3x a week if you use CO2 etc.

Regards,
Tom Barr

[stressed]

hi PeterGwee, may I ask if you say these hobbyist test kits say from SERA, JBL are not good, what sort of kits should we be going for to measure NO3, NH4, etc....

Awaiting your advice.

[PeterGwee]

Lamotte is a good one as adviced by our US friends especially Tom Barr but even then its resolution is only good up to 1-2ppm. But I must warn you that the price is too much for your liking.

You can continue to use your current hobbyist kit but do check the kit for consistency and accuracy. You can try testing your current test kit against a stock solution made out of KNO3 + distill water to see how close the kit gets. Check for consistency as well by testing a certain stock solution several times...how close can you get? I have tried them and was not really convinced although I do use them to check for general high NO3 contributed due to my high bioload (Arggghhh..I overstocked due to my eagerness to beef up my algae crew...I'm going to get algae no matter what I do now as Tom Barr told me unless I thin them out.).

There is also another way of no testing using estimative index method but the method works well only if your bioload is low and does not contribute much NO3 or else things can get worst as I have found out.

Estimative index method (From my own experience:
a)Estimative index method works well when your bioload does not contribute much more than what your plants can take in at moderate to high growth rate.
b)It requires you to find out how much NO3 we have in our tap...not much in Singapore..the most is 7.5ppm with 50% water change which I don't think kiasu Singapore with fussy singaporeans would allow [].
c)Need to do 50% water change and dose 1-3X per week depending on amount of lights. (CO2 injection is a must for this method!)

Good luck!

[naturetan]

Errrrhh... to ensure we check the test kit with higher accuracy, before giving a fair judgement about a particular brand of a test kit company, we need to be very accurate with our amount of additive and solution. Accurate in terms of purity and molecular weight.

This will turn more true when testing are only done in a small sampling. Minute error are prone to magnify. We'll have to consider, is using teaspoon a right apparatus for quality check, before our test could be validated.