Water reading after water change

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Nov 27, 2007
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Our Nitrate level was at 20 before we did a 25% water change. We did the change and the nitrate levels didn't budge, still the same. The ammonia and nitrite levels are still at 0. The only other thing that we did was add a carbon filter to take out rest of medication in the water. My husband said he did scrape off a lot of brown algae around the inside frame of the aquarium, trying to make sure that none of it got back into the water. If any of the algae did get back into the water, would that have anything to do with the nitrate reading??? I know that 20 isn't that big of a deal, but usually when we do a water change it will fall to 10. I tested our tap water and that comes in at 5. All fish are accounted for so what else could have made the change?
 
A 25% water change should reduce your nitrates by 25%. That should take it to 15ppm. Since there is a 10 ppm spread between 10 and 20ppm on the test card. It is possible that it didn't change it enough to make a big difference on the color code. Plus the 5ppm from your tap water.
 
:iagree:
 
We do 25% water changes every week. I am going to test the nitrate again this afternoon and see if there is any difference. Since 20 is not really anything to worry about, I will probably just keep an eye on it and if it starts to rise we will do another water change.
 
I agree with all the above...also how soon after the change did you test ? for some reason I get a delayed reaction to Nitrate after a change, in that after a couple of hours following the test I get the lower reading I would expect, but immediately after there is much less apparent impact.
 
I test my water the next day after a water change to make sure the water has run through the filter and things have settled down. I tested it again this morning and now it looks like the nitrates have actually gone up. We will do another 25% water change and check one of our decorations to make sure no dead fish are in it. We did have a small male danio go missing yesterday, but I think the pictus catfish ate it during the night. After this water change I will test again tomorrow.
 
I think what your getting is with in the accuracy of a color liquid test kit.

Do a 50% change and wait 12 hours to test.
 
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