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A little over 2 weeks ago now I tested the water in my 55 gallon community-planted tank and discovered my nitrate levels were reading at almost 90 ppm. The tank has been set up for several years now, so I at first thought could it possibly be old tank syndrome, however I do 25 to 30% water changes every 2 to 3 weeks. Also the tank shows no signs of anything that one might associate with high nitrate levels in an aquarium. The fish all seem to be very healthy show no signs of any diseases or being stressed and are all eating well and growing rather nicely. The plants are also all doing well and are all very green and growing.The tank has also never had any sign of any type of algae problem.
So I began doing 25% water changes every 3 days ( 6 so far)in order to try to get the nitrate levels down to where they were reading at a safe level, so far to no luck. I've even resorted to purchasing some nitra-zorb around 3 days ago and adding it to the aquarium and so far the nitrates are still reading at almost 90 ppm.At this point I'm simply at a loss on what I need to do next and would appreciate any ones advice on how to best resolve this problem. I've even thought could I possibly be getting false nitrate readings all along. Thanks to anyone for any answers and help you can give.
Ph:7.3,ammonia and nitrate:0, Temp.78

Have you tested your tapwater directly? Ours has 40ppm right out of the tap.

~Michael

Yeah, I actually did that a few days ago and got a reading of 0 ppm.

If the tank has a fairly heavy bioload the water changes should be weekly.

I had the same problem about a year ago, I tried many 25-35% water changes without much luck. Then I went to 50-60% water changes every other day for several times until it was under control. No problems since. Plants that are not rooted to the substrate get their nutrients from the water column, and will absorb more from the water.

Nitrates generally have a cumulative effect. The fish may appear healthy now, but they will be more susceptable to problems later with the high nitrates.

Do test your tapwater though, as mentioned above.

Good luck.

It is possible your test kit could be bad or if it's those strips entirely inaccurate. Make sure to get a reading with a good liquid test kit that isn't too old. If the kit proves to be working or you get the same number with another that's proven accurate then it's probably that the nitrates are beyond your test kit. They are going down but it doesn't register because they are too high for your test to show the proper color on the card. I'd actually do several 50% water changes over a few days if I tested nitrates like that. However you don't want to shock the fish if they aren't used to large or frequent water changes so if the numbers prove accurate I'd start with 25-30% water changes every other day and if it doesn't go down after that do a few 50% changes. Make sure the temp, ph, and other water parameters match the current tank levels and large water changes are not a problem.

Hi,
Once you have eliminated your tap water by drawing a
glass and allowing to sit 24 hours before testing,
look again at your tank.

The nitrate readings result from the bacteria breakdown
of the organic chemicals that result from waste food,
waste from the fish, and any dead or decaying plant
matter. While the nitrate is in solution in the water,
the cause is in the gravel. You mention that you do
regular water changes, but say nothing about vacuuming the
gravel.

The non planted sections of the tank should be vacuumed
from the surface clear down to the glass bottom regularly.
Mentally divide the non planted parts of the tank into
four sections and each week, when you drain off the tank
water, clean the gravel in a section. Next week, clean the
next section, and so on. That way, in a month, you will
have cleaned the gravel in the tank, and at the same time
allowed each section a month to recover, before cleaning it
again.
The primary source of the bacteria responsible for the
Nitrogen Cycle is the gravel bed where the surfaces of each
grain are covered with the bacteria. The next largest source
is the filter, followed by any ornaments and the glass
sides of the tank.

Frank


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