K2SO4 dosage

[tedr108]

Quick question since I am just starting with K2SO4 and am going away for 2 weeks, giving me no time to experiment myself and observe the results...

I'm switching from EI dosing KNO3 to K2SO4, since my nitrates are fairly high ... usually getting to 50ppm the day of my water change.

My standard EI dose for KNO3 is 1/2 tsp 4 times per week. Since KNO3 is 39% K and K2SO4 is 45% K, I'm figuring I can just substitute 1/2 tsp K2SO4 for the 1/2 tsp KNO3. Sound OK to you all? I guess extra sulfur doesn't hurt anything.

When I get back from being away, I'll make sure my nitrates are not too low or too high still, and make any necessary adjustments. I do have quite a few fish in my tank, so it may come down to more water changes if my nitrates are still too high.

Thanks in advance for any advice you can give.

 

[VaughnH]

The obvious advice is to calibrate your nitrate test kit very carefully, using solutions with know amounts of nitrates in them. Otherwise you may not actually have all of the nitrate you think you have. If that is the case you could come back to an aquarium in distress after cutting off the nitrate dosing.

 

[tedr108]

You are wise, Hoppy. I'm not sure I can get those calibration solutions in time, therefore I'll probably go 50-50 KNO3 and K2SO4. I'm actually going to reduce my EI dosing slightly while I'm away because I do not want someone to have to do a full water change in the middle of the 2 weeks -- they are going to do a 10% water change for me, however.

Would those calibration solutions be available at an LFS do you think? I've got time for a quick trip. Or, perhaps the Seachem (or some other brand) Nitrate testing kit has a calibration solution. I'm willing to buy one.

Thanks for the advice.

 

[creighton]

Just curious but what could you use to make a NO3 calibration kit? I have access to a balance that is pretty spiffy, but I'm not sure how to go about making one?

 

[tedr108]

Just did some research and came up with the following:

1g of KNO3 to 500ml of distilled water = 2000ppm Nitrate solution

Add 12.5ml of this solution to 487.5ml of distilled water and you should have 50ppm Nitrate calibration solution.

Here's a link which should support this (if my and their calculations are correct): http://www.barrreport.com/co2-aquatic-plant-fertilization/4051-verifying-recommended-ei-dosing.html.

 

[creighton]

The only thing is the purity. If there was a way to account for that the solution would be a little more accurate. It would be kinda hard to measure 487.5 mls of water really accurately. How much to add to 1 L?

 

[VaughnH]

If you make a 50 ppm solution which is really a 40 ppm or 60 ppm solution, you still have an accurate enough solution to calibrate within the accuracy we need. Use that solution as is for a 50 ppm data point. Mix 10 ml of it with 10 ml of distilled water and you have a 25 ppm data point. Mix another 10 ml of distilled water in that solution and you have about a 15 ppm solution. Etc. That is good enough to avoid thinking you have 50 ppm when you really have 1 ppm.

 

[creighton]

Okay. So how bout this. I'll add exactly 1gram to 1L to get a 20ppm solution. Then I can mail out 1L of water to you all. I'm not sure on the shipping, maybe 500mls would be better. Or better still, if you all have a means to dillute I can mail out a more concentrated solution for you all to dilute. What about a more concentrated Solution? Say a 500ppm solution to dillute down? Let me know what you think would work best.

I guess I'll just use MQ water and the Aquariumfertilizer.com KNO3, but I'll let you guys know if I see anything that may be a little bit more pure at the lab that has nitrate in it and isn't crazy toxic. The balance is accurate up to the nearest milligram so it should be pretty close. And I'll use an Erlenmeyer flask with and etched 1L mark and try to make it as close as possible.

Also, can I do the same with PO4? We have 99.9% pure Potassium Phosphate at the lab so that won't be a problem. Anything else that you all would need to test against a standard? I guess the NO3 standard could serve as a dual K standard if the nitrate ion doesn't interfere with the testing method. I'm so lazy I'll let y'all do the calculations...Its probably pretty bad that I can't do these without looking them up.

Let me know the numbers and I'll do my best to get it out to you guys. It may be a while though. I have finals coming up soon, but I may be able to find some time. School can be such a downer .

 

[tedr108]

Creighton,

I have a friend with a super-accurate scale, so I can make the calibration solution close enough for my needs, since I do have pipettes and beakers. The cool thing about EI is that you do not have to be perfect ... as the name implies we are just "estimating" and that's good enough in the end. Thank goodness!

Good luck on the finals ... I remember those days well.

 

[creighton]

Cool beans. What are you waiting for? Make some calibration solutions! But after all it is estimative...


Hopefully I'll pass all my classes. Electrical Engineering 312: Circuits Analysis is HARD!

The offer still stands for those that would like to try some.

 

[tedr108]

I made a 40 ppm Nitrate calibration solution last nite, since there was a 40ppm color box on my nitrate test card:

Here's what I did:

- 1g of KNO3 in 500ml of distilled water which makes 2000ppm nitrate solution
- 10ml of this 2000ppm solution mixed with 490ml of distilled water produces 40ppm nitrate solution

Personally, I had a rough time telling the difference between the 20ppm and 40ppm color boxes on my card when compared with my 40ppm solution. So, I diluted my 40ppm to 10ppm by mixing the 40ppm 1 part to 3 parts distilled water. The 10ppm color box is much easier to match and I feel the color was almost a perfect match. I think that API did a good job on this particular nitrate test kit for me. At least it should be close enough for what I am doing.

 

[creighton]

Cool. I'll have to try that. What does API stand for? Aquarium Pharmaceuticals Institute?

 

[tedr108]

Yes, you are right about API.

 

[Tom Barr]

Now an accuracy of +/- 20ppm?

Now EI can hit that pretty easily.

This is why I switched to Dry dosing about 10 years ago, no one would make DYI calibration solutions for NO3, K, PO4 etc, and no one would buy a 60$ Lamotte kit.

BTW, you can dilute the sample into the range that is better for any test kit kit also.

Say it(the test kit) is best in the 5-10ppm color range, then dilute: 1part sample to 5 parts DI water etc.

Regards,
Tom Barr

 

[tedr108]

Diluting the sample aquarium water to help in matching my nitrate test color card is an excellent idea, Tom. Thanks.

 

[Tom Barr]

Once you have a set up ref solutions, you can easily see how poor the test kits are and the inherent problem.

You might get lucky and get one that is actually "accurate".
But not everyone else is so lucky......so some will run around telling everyone that all API test kits or whatever brands are accurate and fine.

It's not safe to assume that however. You need to consider the sampling(1 or 2 in most cases), no better than coin flipping

Or the folks that never use more than a single point ref solution and then only 1-2x to see.

Unless you find a problem, you will not see much of a need and be over confident about your test and the method to evaluate it. It very well might be the case that it is not an issue for you personally, but for others and the folks you do give advice to, it may be.

Like aquariums, each test kit is slightly, sometimes radically different.
Generally, even folks that test NO3 weekly etc, rarely calibrate much after 1-2x, or with each new test kit they get. Test kit reagents expire, who knows how long they sit on the shelf at the LFS.

You can get around some of this by measuring frozen water samples(Taken weekly etc) all at once and doing the test all at once along with calibration.
This way everything is the same.

The trade off is that you do not get to adjust and change as go with the dosing etc. You only get to see the final trend over time.


Regards,
Tom Barr