I have justn found out that my nitrate level is between 30 and 50 and nitrite level is about 0.8. These are a little too high. What can i do to get these down a little without affecing the welfare of my oscar fish which seem to be thriving?

You're correct about your Nitrates in my opinion. 30-50 ppm isn't alarmingly high, it simply means you aren't doing enough water changes for your tanks size and stocking level(amount of fish). However, 0.8 Nitrite is tremendously high for an aquarium that ought to be cycled. Your water changes will help to lower this number but that won't address the real cause of the problem. A Nitrite spike can be caused by a number of things, so you're going to have to answer a few questions in order to get to the bottom of this one.

What size is your tank?
What type and how many fish do you have in there?
How big are they?
How often do you feed them?
What sort of substrate do you have?
What type of filtration are you using?
When is the last time you cleaned your aquarium?
What steps do you take in cleaning your aquarium?

I know that's a lot of questions, but I've dealt with high nitrites from many different causes. If you could get back to me on those I can surely offer you a solution.

Well my tank is only 2 1/2 weeks new which means i have only had my fish in roughly a week and a half. It is a fluval duo extra deep 1000 45cm(H) * 100cm(w) * 40cm(D).
I have a external fluval 205 filter. Fine white substrate. Since i have only had it a short amount of time i have only done one water change, (last night) and cleaned the mess up once.
The fish i have are, OSCAR about 3 inches big
4 CLOWN LOACH only about 4cm big
4 guppies about 5cm big
But my oscar fish came to me malnourished from my brother who didn't look after it so i gave it abit of tlc and fed it quite abit to get it back to a healthy state so i was probably feeding it more than a normal person would feed a normal fish.
Am i doing anything wrong here then, considering it is a fairly new aquarium!!?

Well... This situation is pretty grim. Your Aquarium is cycling. The nitrifying bacteria are just starting to build up in your aquarium. Read the article on "How to cycle a tank" in the column on the right of this page. With that many fish in such a small aquarium the Nitrite levels will get much, much higher before they get any better. Clown Loaches aren't all that tolerant of the water chemistry you are about to put them through. This Oscar you have, it actually looks malnourished? I honestly haven't a clue what that would look like. Chances are it's actually sick. There isn't a real good chance that this fish will survive cycling the aquarium either. Sorry.

Another concern is that your aquarium is too small to begin with. Your fish will physically outgrow that tank. Long before that though, you will have this problem all over again as the fish begin to produce more waste than you aquarium can process.

So I guess for now, here's what I'd do. Get the Clown Loaches out of there. Either move them to a different aquarium or take them back to the store. Leave the Oscar and the Guppies. Feed them sparingly but often, very little food, two or three times a day. Do a 25% water change in two weeks. Do NOT disturb the gravel and do NOT clean the filter. (Leave the poo alone) After another month, with a little luck, the tank will be cycled. "Cycled" being when the Ammonia and Nitrite levels are 0ppm. At this point you can start doing regular tank maintenance. Also, start saving for a much larger aquarium.

Add some bio-zyme or ammo-chips to cut back on the ammonia levels. You could quicken cycling by adding small amounts of gravel from a cycled tank into that tank.

Unfortunately, many people don't even know about cycling when they get a fish tank. Fish are at great risk during this period. They are literally being poisoned with their own waste so it's vitally important to keep an eye on those water readings. I don't want to contradict what other people have said but you have quite a high nitrate reading. The bacteria is obviously present. If your tank was in the very early stages of cycling, you wouldn't be getting a nitrate reading. I'm just wondering how high your ammonia has got lately? The higher the ammonia present, the quicker the tank will cycle. Yours has only been going for just over a week. If I was you, get some "prime" this can certainly help divert a disaster if you do get high toxic readings. I have had problems in the past where I've suddenly had a nitrite reading, and sometimes ammonia. I have used prime. I have also got for clown loaches and they are all still alive. What prime does is convert ammonia into a non-toxic form. You will still let reading, it will just not be poisonous to the fish. It also helps with nitrite as well. You can also use it as a water condition.

Keep doing water test every day, ammonia and nitrite especially.

Could you tell us what make of kits you are using? I don't want to patronise you but it's vitally important some of the tests are done properly, especially nitrate.

Even though ammonia and nitrite are deadly to fish, you will actually be amazed how some fresh tolerate very high levels. I was always under the impression that fish would die straight away. That isn't always the case. However, don't be fooled. Even though your fish may not die when you initially cycle the tank, there are very high chances that the immune system has been damaged. In many cases, fish will start dying off at a later date. I have to agree with MNielsen, clown loaches are probably one of the worst fish that you could use for cycling. If you don't get rid of them, keep a very close eye on them for things like white spot. Oscars are also not suitable. They can also be susceptible to diseases at a later date.

You definitely need a larger tank, there is absolutely no doubt about that.

Good luck

OFL... I was working under the assumption that is nitrate in that system would have had to have come from the aquariums the fish were in prior to being in this new one. Chances are when the fish were transfered, the water was transfered right along with them. When I was a kid I got some fish from my aunt to start my goldfish hobby. She actually recommended I take some of her water to help jump start my cycle. Her water was awful. I eventually had to restart from scratch.

In practice, the tank shouldn't be cycled at all, in fact, there should be ammonia still present. Nitrate reading of 50 ppm in an established aquarium means that there is plenty of bacteria going to work. I am rather puzzled at how she is at that stage after just 1 1/2 weeks of having fish in the tank. But you have touched on something that I didn't consider. This is why I ask a question about the test kits. A lot of nitrate kits have to be done properly or you get false readings.

If it came across as I was contradicting you, that wasn't the case

As wrongos tank is cycling i would recommend 25% water changes per day. Altho this will increase the time it takes to cycle the tank it would reduce the fishes exposure to high levels of ammonia and nitrate and would also keep the nitrate down


The tank the fish are in at the moment is perfectly fine but a new tank will be needed sometime in the future as the oscar get bigger. Also wrongo do you realise the oscar will eat the guppies when he gets bigger!!

Mneilssen i dont see how a nitrate reading of 30-50 can come from tank water the fish were transfered in. His tank is roughly 6.5 square feet. If the fish were transfered in bags or even buckets and were kept in poor condition that still wouldnt leave a nitrate of 30 to 50. The tank has either cycled quickly or something else is up

The missing piece of the nitrate puzzle to me here is the exact condition of the aquarium that the "Malnourished" Oscar came from. The water could have been awful. (200ppm+ nitrate) It is feasible that the Oscar could handle such high levels if the increase came gradually over time. The description in Wrongo's other post that the fish lacked energy and lost its color could certainly be a sign of heavy Nitrate poisoning. I've see this in my own small goldfish tanks. Nitrate isn't super toxic. It takes a heck of a lot of it before you really start seeing a problem. If his brother truly didn't take care of his tank then anything is possible.

OFL hit on a biggie with nitrate tests, which is that you must follow the directions precisely. I myself have forgotten before to do the 30 sec of shaking the second bottle with my Aquarium Pharmaceuticals test and came up with an impossibly low result. That's the only Nitrate test I am familiar with, but there certainly could be others that would show false positives.

In my wild and woolly days back when I started keeping fish I "cross-contaminated" my tanks on a somewhat regular basis. I had a 2 quart (approx. 2L) pitcher that I used to transfer a fish from a new tank to a cycled tank. The New tanks ammonia wasn't coming down and this poor guy was suffering at 8ppm. That amount water alone was enough to bring the healthy aquarium's nitrite higher than my tester could show results in just a few hours. Obviously this little cautionary tale doesn't quite apply in the reverse. It's just an example of the trouble you can get into when you start mixing water from two very different tanks.

OFL I'm not one to get offended by contradiction. A good clean argument (in the sense of discussion) olny makes everyone involved smarter!

Thanks for all the help guys i appreciate it. I dont want to start adding chemicals right now, i want to see if it sorts itself out naturally.
All the fish though, especially the oscar, seem to be absolutely thriving right now. I have not seen the oscar this active for AAaaaages and it is eating very well. It feeds out of my fingers and dances on the front glass when ever i am in the room. This surely is a good sign, is it not?
As for the make of my tester kits, they are NUTRAFIN test kits BUT the colour charts for reading the levels off are very closely matched (apart from the 2 extremes) so it is hard to get the right result. Also the colour chart has quite high differentials between the toxin levels (if you get what i mean?)I am sure i will get there eventually with experience.
Does anyone think that these tester kits are no good? I think i paid £21 for the four kits? Anyone got any expressions on this?

MNeilssen wrote:


I have used various nitrate test over the years, however, aquarium pharmaceuticals is by far my favourite. The fact that you only use two bottles and the tests only take around five minutes to come through is favourable to me.

You are absolutely correct, not shaking the bottles correctly will result in very low nitrate readings, at some time zero. This has happened to me on a couple of occasions. However, when you start keeping Oscars, you will realise that occasional high nitrate is part of keeping these messy fish. So I will warn people, if after a week, you get a nitrate reading of zero, do the test again.

I often see people boasting about having zero nitrate readings. I'm willing to bet they haven't done the test properly.

If you want to cut down the tank maintenance, I would suggest getting a very large tank. ("You" meaning our general audience, not you personally M)