Nitrates won't go down no matter what I do.

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Hi, I have an 18.5 gallon aquarium (70l). It is stocked with 4 neon tetras (I know this is not enough, I used to have 8 but there was a neon tetra disease outbreak, I do not want to get more because I can't seem to keep them alive for more than a year), 5 corydoras, 2 honey gouramis and 3 otos. I have a filter that came with the aquarium, and a sponge filter I added. I have tons of live plants, mostly hornwort and anibius.

On Saturday I added the otos, I tested my water for the first time in a while because I know otos are sensitive. Everything was perfect exept nitrates. They read 40ppm. I did a 50% water change after the test. On Sunday I tested only nitrates, they read 40ppm. I decided to clean my filter and do 20% water changes daily for a week or so, to see if that helps. The next day, on Monday I tested my water. 40ppm nitrates. I did a 20% water change. Today I tested my water, 40ppm again. I tested my tap water twice, both read 0ppm of nitrates. I have tried feeding less also. I'm very confused, I feel like I have done everything I can. Any other suggestions?

Separate topic:
A lot of you may remember me from a few years ago, you were right, my tank was not cycled, a lot of fish died. For the past year it's been really good though, basically no problems (asides algae, can't get rid of it), the algae may be a product of the nitrates though. The otos might help with the algae to. I really want to keep the otos alive so that's why I made this post.
 
seems strange that your nitrates are high, but your tap water is zero, & you've done the normal stuff... maybe try adding a plant or two???

wondering if you are on city tap water, & what you are using to remove chlorine??? & in what form ( if on municipal water ), they are adding chlorine... most are using chloramine, but maybe something newer??? but maybe could be a biproduct or chlorine removal???
 
You have tested your tap to see if it's polluted from the source? A lot of people who live in areas with intensive agriculture have trouble with their water.

If the tap is good, I'd rinse my filters. And beyond that, check my water test kit, and keep doing changes.
 
Hi, I have an 18.5 gallon aquarium (70l). It is stocked with 4 neon tetras (I know this is not enough, I used to have 8 but there was a neon tetra disease outbreak, I do not want to get more because I can't seem to keep them alive for more than a year), 5 corydoras, 2 honey gouramis and 3 otos. I have a filter that came with the aquarium, and a sponge filter I added. I have tons of live plants, mostly hornwort and anibius.

On Saturday I added the otos, I tested my water for the first time in a while because I know otos are sensitive. Everything was perfect exept nitrates. They read 40ppm. I did a 50% water change after the test. On Sunday I tested only nitrates, they read 40ppm. I decided to clean my filter and do 20% water changes daily for a week or so, to see if that helps. The next day, on Monday I tested my water. 40ppm nitrates. I did a 20% water change. Today I tested my water, 40ppm again. I tested my tap water twice, both read 0ppm of nitrates. I have tried feeding less also. I'm very confused, I feel like I have done everything I can. Any other suggestions?

Separate topic:
A lot of you may remember me from a few years ago, you were right, my tank was not cycled, a lot of fish died. For the past year it's been really good though, basically no problems (asides algae, can't get rid of it), the algae may be a product of the nitrates though. The otos might help with the algae to. I really want to keep the otos alive so that's why I made this post.

You mention your tap water has 0ppm of nitrates, which sounds correct as Sydney has very high standards of tap water. But it’s strange that you can’t get your aquarium water to below 40ppm.

What I suggest you do is to do a test before a water change, then change 4 buckets or 40 litres of water and test again immediately after the water change. If there’s no change in nitrates before and after the water change, then I suspect your test strip or API Master test kit has reached its expiry date, or you didn’t rinse and clean the test tubes well enough, or you didn’t shake the nitrate bottle #2 hard enough.

You also mention you have tonnes of live plants, so there’s no reason why nitrates should remain high.
 
If your testing supplies are fresh and you are sure you are following directions carefully, I would have the water tested somewhere else, like a friend or a fish shop. Not hard to jar up a bottle of your tank water you just tested yourself. On a side note I do find it challenging to read the nitrate colors. I am on the very low end of the nitrate testing range, and it usually looks similar. I did a 35% WC yesterday and the before and after test vials look the same 5ppm to my eyes. The color change from 40 to 80ppm looks similar to me as well. My kit is brand new and tests fine on my other tanks that are cycling. My guess is you actually are dropping your nitrates some with WCs, continue your diligence as 40 is high for a lot of species. You could be dropping your nitrate from 75 down to 35 and it is not going to look a lot different on an API kit. If you aren't already, I would save the before WC vial so you can compare it to after test?
 
Hello. The water in such a small tank needs to be changed twice weekly. Gradually work up to the point you change half the water a couple of times a week. This will maintain a steady water chemistry and this is really all the fish need.

10
 
sensitive. Everything was perfect exept nitrates. They read 40ppm. I did a 50% water change after the test. On Sunday I tested only nitrates, they read 40ppm. I decided to clean my filter and do 20% water changes daily for a week or so, to see if that helps. The next day, on Monday I tested my water. 40ppm nitrates. I did a 20% water change. Today I tested my water, 40ppm again. I tested my tap water twice, both read 0ppm of nitrates. I have tried feeding less also. I'm very confused, I feel like I have done everything I can. Any other suggestions?
Did you vacuum your gravel?
 
Your largest water change was 50%. This is my normal weekly change. When I have a problem I do 75% so this (or 80/90%) is what I suggest you do.
Also watch your feeding quantity to ensure that you aren't rising the levels with food.
Welcome back! :)
 
Hello again. If nitrates are this high in your drinking water, then I'd start looking for something else to drink. A hardy fish species isn't going to notice nitrates at this level. But, you don't want the level to go much higher or you start seeing a drop in reproduction. Just remove and replace the water more often then once a week and replace half or even a bit more. I would also look at adding some Dwarf Water Lettuce to the tank. This plant is a very good, natural water filter and will reduce the nitrogen in the water.

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Hello again. If nitrates are this high in your drinking water, then I'd start looking for something else to drink. A hardy fish species isn't going to notice nitrates at this level. But, you don't want the level to go much higher or you start seeing a drop in reproduction. Just remove and replace the water more often then once a week and replace half or even a bit more. I would also look at adding some Dwarf Water Lettuce to the tank. This plant is a very good, natural water filter and will reduce the nitrogen in the water.

10
I think he said his tap is zero nitrates?
 
Hello. That's good. Our public water people would have a fit if there were nitrates at the level we're talking about in our public water supplies. Keep the water chemistry steady with large, frequent water changes. Nitrates at 40 ppm is a bit high, but not a problem for a hardy species of fish.

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