Hi all, I've had my 20 gallon tank set up since september and i have 2 goldies living in it. I believe my tank cycled over a month ago because the nitrites are down to 0. Unfortunately my nitrates have continud to remain high. I test the water every week or so and they are always around 40ppm. I change the water sometimes twice a week (about 25% each time) and still they will not go down. I usually change the water by vacuuming, is this a bad idea? I also replaced my filter cartridge yesterday with a biobag cartridge (I have a topfin 20 filter). I'm hoping the new kind a cartridge will help with my cycle... any advice would be appreciated.

Also, my pH has constantly remained really low. I've tried to raise it once by adding baking soda (didn't do much) and I've been using "proper pH 7.0" every week with water change and it still stays under 6.4. My goldfish seem healthy, although my oranda has seemed more lazy than usual.

Have you checked the nitate levels out your tap if thats were you get your water from hun?

What is your filtration like hun how much water does it move for you and hour?

IS the water moving good at the top of the tank?

How much do you feed your fish and do you have any live plants in the tank?

Well, I'm not exactly sure on the amount of water cycled per hour because I no longer have the box the filter came in, but I think it was around 150? The readings of my tap water are:
5-10 ppm nitrates
0 nitrites
50 ppm alkalinity
6.8 pH
The surface of the tank does move pretty well from the power filter and the bubble wand. I feed my goldies once a day with Hikari sinking pellets and goldfish flakes about once a week.

also, I don't have any live plants.

There are a couple of things working against you here, most likely. As you found, and Koko advised, your tap water itself has nitrates in it. So you are never, ever going to be able to get lower nitrate readings than 5-10 ppm nitrates.

Secondly, when you do a water change you need to actually look at the dilution that you are doing. For example:

If your tank water has 40ppm nitrates and you change out 25% of the water, you would be lowering the nitrates to 30ppm. But since you are adding back in water that already contains nitrate to the tune of 5-10 ppm, you are probably going to only lower the overall quantity to approx. 34ppm. In a drop test kit, the difference between 40ppm and 34ppm in not possible to see. So it seems as if nothing changes. You also have to remember that the fish are constantly adding more ammonia that is constantly being converted to nitrate - a continuous source.

Since you cannot change your tap water, you should, perhaps, change your water changing habits. I would suggest that you start doing 50% water changes each week - up to 75% water changes if necessary. As long as your beneficial bacteria is contained in your filter well, and you have a solid platform that you do not disturb, you will not bump or even nudge your cycle by changing large amounts of water. (IF you were to change 100% you would still have 5-10 ppm).

It is possible to help reduce nitrates by eliminating all possible pockets of waste that may or may not be properly cleaned each week. If you have a cannister, you need to empty out the reservoir of water in the bottom of this. Leave the bacterial platforms alone, but clean the yuck out of the bottom of the filter. IF you have gravel, reducing the amount or eliminating it can also help to a degree.

I think if you simply up the volume of water that you change each time, and perhaps decrease the times between changes you will get things back into shape.

That makes a lot of sense, thank you! One question, when you said to empty the filter cannister, do I just dump all the water out and leave the filter the way it is?

MOst cannisters are built such that there is a reservoir of water that is in the bottom of them. The media makes the water slow or swirl such that the larger solid waste particles fall out of solution and sink to the bottom of the filter box. The smaller particles are caught by a gross or fine filter floss of some nature. That reservoir can have a fairly large volume of solid yucky waste in it after a short time - even a week. This waste still produces ammonia for the bacteria to process - the end product being nitrates. Any source of ammonia that you can remove from the tank pre-cycle will prevent nitrates from being created and help lower the nitrate values.

You do not want to disturb whatever platform you have in your filter that holds the populations of beneficial bacteria, though. Ceramic cylindars, sintered glass, lava rock, bioballs, sponge, etc. all should be left, and only the gross waste from the bottom of the filter box being dumped.