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Discussion Starter · #1 ·
I've been doing EI low-light/weekly dosing for about a month using dosage recommendation from the sticky and I am having trouble keeping my nitrate levels from rising too fast. They are easily getting up to 40 ppm within the week between water changes. I re-tested my tap water and found I have 5-10 ppm coming out of the tap.

If I reduce the amount of KNO3 I am dosing, how would I figure out how much to increase K2SO4 to replace the reduced Potassium?
 

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interesting. i just mixed new PPS fert with no KN03 because my nitrates are too high.

Didn't even think about the potassium because I'm just not a chemical person at all. I just mix what I read.
 

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Discussion Starter · #4 ·
Thanks, I'm pretty close to fully stocked.

I came across a pretty cool chemistry site (http://www.webqc.org/mmcalc.php) and according to it KNO3 is ~38% potassium by mass and K2SO4 is ~44% potassium by mass. So if I add a slightly smaller quantity of K2SO4 than I remove of KNO3 I would come out about even on total potassium.

I don't think I'll do that much K2SO4 since I don't want to build up too much sulfer over time, so I'll add maybe 1/4 the amount and increase it if I start seeing signs of potassium deficiency.
 

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Yes, the amounts are just a bit different. I just swap them back and forth depending on how much NO3 the tank needs. But you are right to cut it down a bit.
 

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Discussion Starter · #7 ·
So it's been about I week since I last posted here. I re-mixed my macro solution to exclude KNO3 and did two 50% water changes in that time but can't seem to get my nitrates below 80 ppm according to my API test kit. I got a pressurized CO2 system this week and I'm hoping that will help the plants metabolize the existing nitrate more quickly. Is that a reasonable idea as long as I keep the other macros and micros available?
 

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Discussion Starter · #9 ·
whats that same API nitrate test read on your tap water?
It's reading between 10 and 20 ppm from the tap. So I know that's as low as I can go without buying an RO/DI filter.

When I first got worried about the nitrate levels it was at over 100 ppm. By my back-of-the-envelope calculations if I had 120 ppm and did a 50% water change with 20 ppm tap water it should have taken me down to 70 ppm and a second 50% water change should have taken me down to 45 ppm, but that hasn't been the case so far. Do those figures sound like a correct estimation?
 

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I think your numbers are in the right ball park.

Have you callibrated your test? There are many posts here where people have found the API Nitrate test to be off by double or even triple! Either direction.
Test results for any amount over about 20ppm are difficult to read. Can you tell the difference between all those hot pink-rose-fuchsia shades?

You are right:
If you do a 100% water change, and the new water has 20ppm NO3 then your first test ought to be really close to 20ppm, probably not higher than 25ppm. Some water is still in the tank, even if you drained it down until the fish are flopping, and there is often some NO3 lingering in the substrate that will show up in the water when you refill.


Here is what I would do:
1) Calibrate the test.
2) Add zero NO3 from fertilizer.
3) Couple of more big water changes, back to back.
4) Test the NO3. This is the base line. The lowest you can get the NO3 without taking more measures (suggested below).
5) Monitor it daily. Any rise from here on is from fish food.

Fish food supplies reasonable amounts of N, P, and most traces. If the plants are not even using up the amount of NO3 you are adding from fish food, then they are probably also not using the P or traces from fish food.
You might just need to dose K, Fe and CO2 for a while.

Other ways to lower the NO3:
Run your tap water into a garbage can.
Hook up a filter with some nitrate removing pads, zeolite or similar materials.
Test daily until the NO3 is significantly less. Then use this water for water changes.

Run your tap water into a plants-only tank that is set up with LOTS of light, and a good supply of other nutrients. Grow emersed plants so you don't have to worry about CO2.
When the NO3 is significantly lower, use this water for water changes.

Bump: Another thought:
If the NO3 is so high in the tap water, I hope you are not drinking it, and especially no children are drinking it!
 

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thats pretty high from tap water, might take a bit of tank and tap water down to your LFS and see if they test it the same.. if its really that high you should of never been dosing nitrogen extra imho.. you could be off the charts high and your WC calculations would be off.. I dont think the API test is all that accurate at high levels like @Diana suggested, do a couple more PWC's and see if there coming down..

some bad test solution can have you chasing problems that dont actually exist.
 

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Discussion Starter · #12 · (Edited)
Thanks, that's a lot of helpful information. You're definitely right about the higher test values being hard to read

I'll have to pick up some distilled water to calibrate the the test, but I can probably do that tomorrow. Hopefully it will show that the test is reading far too high since, as you said, I have been drinking the tap water here for years. I found a city water quality report (2 years old) which said the city water supply ranged from 0.28-1.2 ppm which seems much more reasonable than the 10-20 I measured. I think I will take my water down to the pet shop as well to have them check it.

Edit:
Could it be that something else in the water is reacting with the test solution and causing a false nitrate reading? We do have very very hard water here.

Edit 2:
Also found that the EPA restriction on nitrate in drinking water is a maximum of 10 ppm. I couldn't find any record of the city failing checks so I don't think the water is nearly that bad.
 

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Last checked my nitrates with uncalibrated API test kit a couple year's ago after beginning the dosing of KNO3 for my own low tech NON CO2 tank(s) and reading was around 120ppm.(near as I could tell)
A couple 50 % water changes and reading was 80 ppm.
I did not bother to calibrate the test kit,just put it away and bought a bunch more plant's along with reduced feeding's.
Big difference between nitrate readings as result of accumulated organic 's, and nitrate reading's as result of adding inorganic mineral salt's.
I add quite a bit more KNO3 now than I did when I first began dosing cause plant mass increase resulted in the need for more according to plant's.
I just try to keep the organic waste to a minimum with water changes ,cleaning the filter frequently (3 weeks)
Plant's ,fishes,shrimp's thrive for me.
 

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Yes, NO2 can affect some tests. But if your water had NO2 your fish would not be thriving.
Plant's would much prefer the NO2 over KNO3 but as you say,,the fishes would not like it.
Some folks a while back on another forum were all keen to add a special fertilizer containing Urea to their tank's.
Those who did so realized that in their plant only tanks ,growth improved .
They could have got the same effect by adding a few fish.
Those who already had fish/shrimps in their planted tanks tried the urea with expected result's (ie) dead fauna.
 

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Discussion Starter · #16 · (Edited)
Thanks again for the info. My Nitrite test is coming out negative, so I don't think that is a problem. I had been curious about how safe fertilizers with urea and ammonium nitrate were for fauna but haven't tried any even though I know a lot of people use them.

I did another 50% water change last night and tested nitrates this morning with a result of 40 ppm. I'm going to get some distilled water tonight and try calibrating the test since I now suspect it is reading way to high.

I've also noticed over the last couple days that algae growth has increased which makes me wonder if the test is way too high and my nitrogen is now actually too low relative to the other nutrients.

I read up on how to do the test calibration but have a question. I found a forum post where someone posted a response email from API about nitrate test kit accuracy. API said to be sure to compare the reading the proper amount of time after mixing (3 minutes) since the reading could continue to increase to incorrectly high levels over a longer time. I've been careful to do this in my testing but I'm wondering how I can preserve the results of my calibration samples for later comparison. I don't think a photo would be accurate enough since most digital cameras now automatically compensate for the yellowish lighting we have indoors and tend to be naturally over sensitive to red which they also try to auto correct, but I doubt they do well enough for a test reference. I thought of just keeping one as my target nitrate level and then letting my test samples sit a couple hours before making too-high/too-low comparisons to that, but my samples I have tried letting sit all get so similar after a while I don't think I could tell the difference and I imagine the variability of the inaccuracy will increase as well.

Any suggestions for saving calibration results for reference?
 

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Discussion Starter · #17 ·
Ok, so I mixed up the calibration reference solutions and it looks like my tank is actually in the 5-10 ppm Nitrate range although the two references are nearly identical. Much better that what it was saying with the reference card!
 
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