[Nodalizer]

I do weekly 25 Percent water changes. My filters have both been cleaned in the last month, using guidelines I found on here or the tropical fish keeping site, using water from the aquarium, etc.

I know its confusing, but a weekly change of 25% will result in high nitrates, even though you have been recommended to do it, I will explain.

Each time you change the water (any amount) you are left with some nitrates in the water, this then added to the new nitrate from the next week means next time you test the tank the nitrates will be higher again.

This will keep adding up until they are out of control like you have now. So what to do ?

You need to do a bigger water change every time you see the nitrates getting to high. Too high would be more then 15-20pmm. After that big water change just go back to your normal water changes.

The size of the bigger water change depends on how out of control they got. I would say 50% would be a big enough water change for a nitrate balance on a tank that does weekly changes of 25%.

I will probably try the smaller water changes more frequently, but I've killed fish doing a 50% water changes.

If you kill fish doing a large water change it can be because of a number of things, but most likely you have a lot of stuff in your substrate that is not getting vacumed up each water change, when changing the water, it needs to be big enough to allow you to get all of the mess out of the substrate.

When you add the big amount of water and it stirs up all the mess you left behind on previous cleans it would create an ammonia spike, which will kill fish. This is not the water changes fault but not cleaning properly the last few times.

and my nitrites were at 0.5. What should I do, other than my weekly water changes to bring these levels down?

I would say your nitrite problem is because of what I said above, I think you are not cleaning the bottom of your tank properly, and each water change you are causing an ammonia spike which will need to higher nitrites.

High nitrites can stop or kill the benifitial bacteria that convert that nitrite to nitrate. You will need to get that nitrite down with water changes (now, not weekly), as many as is needed IMO.

I hope that helps.

 

[Nodalizer]

I think you missed the point of my post. I wasn't talking about amount or frequency. I was talking about nitrate creep, which happens in EVERY tank, and we fix almost second nature, but someone having problems needs to know this effect will happen and account for it.