Raising Salinity = Raising Nitrates?

[By_a_coo]

Hi all,

Sunday I did a 50% WC in my GSP's tank, my target is 1.008-1.010 and I'm raising the salinity by 2g/L of salt weekly. My tap water has no nitrates, after the salt mixed I read some nitrates (2,5 mg/L).

I found this chart, as you can see, some brands of marine salt have nitrates in it:



Now what? If we do WC to reduce nitrates.

[RTR]

Nitrate at 2.5 mg/l or 2.5 ppm is relatively trivial for our purposes.

[By_a_coo]

Now, add the amount the fish will generate along the week...

If the nitrates increased with the addition of 2g/L of salt, imagine when I increase the salinity to 15 g/L.

2g/L -> 2,5 ppm of NO3
15g/L -> ~18 ppm of NO3 (plus what is weekly generated by fish)

[Myaj]

Did you test that right away or let the water sit for a bit? Just curious.

I've never noticed my tank nitrates go over 10 and I've used Instant Ocean for a few years...

[By_a_coo]

I tested the next day after I did the WC.

[Myaj]

Huh, that's strange.

[Little_grey_puffer]

Thats very odd as everytime i have done a water change, my levles are always less than 2 in my marine tanks even with a high salanity of 1.023. This is very interresting as i am perplexed as to how this can be with top quality salt mixes of brands we all love and trust.
How much salt did it say you have to use till it raises the nitrate level by that much on padge you found the chart?
Did you mix the salt in the same bucket you water changed with?

[By_a_coo]

Did you mix the salt in the same bucket you water changed with?

No, I have a container where I only mix the salt with new water and nothing else. The water from the tank goes straight down the drain.

How much salt did it say you have to use till it raises the nitrate level by that much on padge you found the chart?

If you were refering to this:

2g/L -> 2,5 ppm of NO3
15g/L -> ~18 ppm of NO3 (plus what is weekly generated by fish)

This is an account that I figured based on the nitrate test results I read one day after the water change. I guess there are some nitrates in the salt I'm buying. I don't how much nitrates that brand of salt I'm using can have in it. I will test the nitrates again on sunday - WC's day - before the WC and right after the WC. I'll let you know the nitrate test results since I'll raise the salinity a little more... we'll see if the nitrates will increase too.

[Little_grey_puffer]

Yeah good idea. Post the results and let us know what you find.

[RTR]

Test the pre-mixed salt before it goes into the tank, as well a the tank before and after the addition. That way you can track the nitrate levels.

Don't expect numerically perfect results - our test kits do not read that sharply.

[By_a_coo]

Test the pre-mixed salt before it goes into the tank, as well a the tank before and after the addition. That way you can track the nitrate levels.

Testing the pre-mixed salt water will be better to check if the salt has nitrate. I'm glad you pointed it!

Don't expect numerically perfect results - our test kits do not read that sharply.

You're right! The test kits aren't so accurate, they are?

[By_a_coo]

I think I've been making mistakes about the nitrates level.

Today I tested every water samples.

Tap water: zero nitrate
Pre-mixed salt: zero nitrate

The GSP's tank:
One week ago (I raised salinity to 2g/L): 2,5 mg/L
Today before the water change: 2,5 mg/l
Today after the water change (I raised salinity to 4g/L): zero mg/L

I think that nitrate traces (2,5mg/L) came from the water that was in the filter used in my planted tank where I used to dose too much nitrates.

Sorry for the mess!

[RTR]

Never apologize for asking a question - It is the way we all learn, and why we are all here.

The tests are actually accurate enough for the way we use them. Most are color scales with non-trivial differences between steps. That means that the "end point" is not really a point but a blur - frequently from 1/2 the scale number to either 2x or more of the "read" value. Looking at it that way it sounds awful, but for many uses it is actually not bad at all. We do get a lot of info out of these tests, and we really have little or no need for photovoltaic accuracy. That is for the research labs.

HTH

[Little_grey_puffer]

I am glad that its all sorted out for you now
RTR's right, we only learn by asking after all.

[By_a_coo]

That's why I thank everyone so much!