Cycling tank

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TFrost19

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May 16, 2025
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I have been cycling my 20 gallon for over 2 months and I can't get my nitrites to lower. I have done water changes and added Dr. Tims one and only and my nitrites still very purple.
 
I have been cycling my 20 gallon for over 2 months and I can't get my nitrites to lower. I have done water changes and added Dr. Tims one and only and my nitrites still very purple.
What are your full water parameters? Need to know pH, ammonia, nitrite, nitrate, GH, KH and temperature. (y)
 
Hello. 20 gallons isn't very much water and the chemistry can be much less stable than the water in a larger tank. The key to keeping fish healthy is to keep their water clear of their dissolving waste material. A 20 gallon tank will do well with a 50 percent water change performed every three to four days. Of course, doing this even more often is better. If I was keeping such a small tank, I wouldn't keep very many fish in it and make sure I kept smaller fish. I would remove and replace half the water at least twice weekly. Feeding should be minimal. A fish stomach is about the size of one of their eyeballs. So, it doesn't take much to fill it. A larger tank, at least 30 gallons wouldn't take quite so much work, but a smaller tank can work. You just need to pay closer attention to the water.

I once cycled 50 gallons of water with a dozen Buenos Aires Tetras. I simply removed and replaced half the water every few days and kept the food to a minimum. The tank has been running for about three years and there are 22 of the tetras in the tank. I've just followed an aggressive water change routine and the fish are all big and healthy.

B
 
Don't you have to feed Dr. Tims one and only? What are you keeping your ammonia level at?
You need to understand the ecology of the aquarium and what the cycle means. In short: when you have 0 ammonia and nitrites after they went up and down, there are enough microbes to handle the ammonia load that is present from the livestock in the tank. The method BBradbury is using and describing is not letting the ammonia level ever get high enough to be toxic to the fish. You don't need much in the way of nitrifying microbes if you never have enough ammonia to feed them. There are cases where fish can live in tanks that never " cycle" because the water's pH is so low, nitrifying microbes can't live. The plus side to these setups is that there is no nitrites or nitrates because the ammonia ( which is actually ammonium at those lower pH levels) never gets converted. The down side is that the fish are living in water that is higher in their " bodily functions" in between water changes and you need to be doing water changes frequently to remove those excretions unless you have things like plants that can utilize them or livestock that feeds off the feces.
The one downside to BBradbury's method is that you HAVE to adhere to a strict schedule of high volume water changes if you fully stock the tank so that it keeps the ammonia level low. But say you go on vacation and no water is being changed during that time, the possibility exists that the current stock in the tank could overwhelm the present biological filter bed while you are away and the fish die off if it gets too high. Keep in mind that there are nitrifying microbes present in a tank, with a pH higher than 6.0, but if your ammonia level never gets higher than say, .15ppm because you are changing the water so frequently, the tank is only cycled for .15ppm of ammonia production even if your bioload is producing say, 5 ppm of ammonia. That's fine if you keep the ammonia level that low. It's not fine if you can't. In today's busy world, not everyone has the ability or the willing to be doing water changes as frequently as necessary as B describes so they rely on a larger biological filter bed to do the work. Both methods work because of how they work. And that's the short version. ;)
IMO, there is always a plus to changing water especially since many of the fish we keep have an ancestry that comes from moving water so they are always in good clean water. (y) I don't know how this theory of only changing water because of the nitrate level got started but you change water for so many other reasons than just the nitrate level. I do/ did it religiously weekly or more often depending on the fish which is why, I believe, I have been as successful at fish keeping and breeding as I have been. (y)
 
Hello again. Andy is correct about the dedication required if you decide to follow such an aggressive water change routine. I don't think more than one in 10,000 or so tank keepers would consistently follow it. However, you won't find a more balanced water chemistry, nor healthier fish if you can do it. I have 10, large tanks and have been changing out most of the water every few days for a lot of years. I don't do vacations, but I've been rewarded with Tetras that are six years old, Plecos that are eight, Guppies live to four, Platies at least four and Corydoras that are seven years old. I can even get Feeder Goldfish to approach 8. So, to me, the water keeping hobby isn't just a part time interest, it's a long term commitment.

B
 
Hello again. Andy is correct about the dedication required if you decide to follow such an aggressive water change routine. I don't think more than one in 10,000 or so tank keepers would consistently follow it. However, you won't find a more balanced water chemistry, nor healthier fish if you can do it. I have 10, large tanks and have been changing out most of the water every few days for a lot of years. I don't do vacations, but I've been rewarded with Tetras that are six years old, Plecos that are eight, Guppies live to four, Platies at least four and Corydoras that are seven years old. I can even get Feeder Goldfish to approach 8. So, to me, the water keeping hobby isn't just a part time interest, it's a long term commitment.

B
Definitely. With one of my hatcheries, I didn't take a vacation for near 13 years. When it closed, I took about 15 vacations over the next couple of years. LOL (y)
 
Thank you both for all your input I learn a lot from you both along with Aiken. It looks like we just don't know enough about TFrost19 water. I was thinking he is not cycled (I don't know) and has no fish (don't know this either) and that Dr.Tims One and Only needs a food source to keep the nitrifying microbes alive until the tank gets fish. Without knowing the other water parameters (like Andy ask for) I don't understand why the nitrItes are not changing. I must be missing something in the OP.
"I have been cycling my 20 gallon for over 2 months and I can't get my nitrites to lower. I have done water changes and added Dr. Tims one and only and my nitrites still very purple."

 
Thank you both for all your input I learn a lot from you both along with Aiken. It looks like we just don't know enough about TFrost19 water. I was thinking he is not cycled (I don't know) and has no fish (don't know this either) and that Dr.Tims One and Only needs a food source to keep the nitrifying microbes alive until the tank gets fish. Without knowing the other water parameters (like Andy ask for) I don't understand why the nitrItes are not changing. I must be missing something in the OP.
"I have been cycling my 20 gallon for over 2 months and I can't get my nitrites to lower. I have done water changes and added Dr. Tims one and only and my nitrites still very purple."

The thing is the OP's test kit may be faulty or the reagents bad and the complete panel can bare that out or confirm it's correct. The nitrifying microbe that converts nitrite to nitrate has parameters that will make them reproduce faster and if the OP's water isn't within those parameters, that too can explain the slow reduction. That's why you need to know all of it, not just some of it.
 
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