water change amount

cf17 · 01/17/2015, 12:12 AM

Hello, I am just wondering how much % water I should change per week. I have a 90 litre (24 gallon) tank with two clownfish and a bicolor blenny. There is about 20lb of live rock. I have been changing 1/3 water per week but the nitrate level has stayed around 15-25. What level nitrate can these fish tolerate?

I have seen recommended water changes of 10% per week, so now I am not sure if I have been changing too much water or not enough?

Thanks.

FraggledRock · 01/17/2015, 12:30 AM

I would change when your parameters are becoming problematic.

excessive ammonia, nitrite and nitrate.

weekly is recommend 5 - 10% so youre looking at about 5 gallons.

did you cycle your tank before adding fish?

also nitrate is the end of the nitrogen cycle, so that will keep happening (faster nitrate production) espcially in a smaller water volume environment

cf17 · 01/17/2015, 12:55 AM

Yes, I cycled the tank for a month before adding fish. How much nitrate is excessive?

FraggledRock · 01/17/2015, 12:59 AM

Probably around 25 -50 but try to reduce it asap

gone fishin · 01/17/2015, 07:08 AM

If it is a fish only I would not sweat the 15-25ppm of nitrate. If it got up to 50 or so then I would take more aggressive action. A lot of fish can tolerate very high levels of nitrate. I would guess you have in the neighborhood of 15-18 actual gallons of water. IMO you have a pretty good bioload in that tank, so nitrates could be an ongoing issue.

dkeller_nc · 01/17/2015, 08:55 AM

As it turns out, water changes aren't a good way to handle nitrates on an on-going basis. Large one-time water changes are an effective way to immediately reduce the nitrate concentration in a hurry, however.

A better way is with the utilization of an aggressive skimmer and carbon dosing. This article will get you started with what you need to know. I do this regularly in all of my tanks, even my 20g nano. I dose about 1.5 mL of vinegar daily when I feed the fish in this tank and nitrates remain undetectable.

cf17 · 01/18/2015, 04:44 PM

Okay I will try vinegar and see how that works out.

I was also thinking of getting some more live rock this week - would that help reduce nitrate?

dkeller_nc · 01/18/2015, 04:52 PM

No, at least not directly. The carbon dosing does two things - it encourages anaerobic denitrification bacteria in regions of your tank that are anoxic or at least low oxygen - that would include the bottom part of your sand-bed (if you have one), and the deep parts of porous live rock. It also encourages bacteria growth overall. Since bacteria require nitrogen and phosphorous to grow and reproduce, and your skimmer removes them from the tank, the effect is to reduce both nitrate and phosphorous from the water column.

01/17/2015, 12:12 AM	#1
cf17 Registered Member Join Date: Nov 2014 Location: Australia Posts: 26	water change amount Hello, I am just wondering how much % water I should change per week. I have a 90 litre (24 gallon) tank with two clownfish and a bicolor blenny. There is about 20lb of live rock. I have been changing 1/3 water per week but the nitrate level has stayed around 15-25. What level nitrate can these fish tolerate? I have seen recommended water changes of 10% per week, so now I am not sure if I have been changing too much water or not enough? Thanks.

01/17/2015, 12:30 AM	#2
FraggledRock Registered Member Join Date: Dec 2014 Location: New York, New York Posts: 2,185	I would change when your parameters are becoming problematic. excessive ammonia, nitrite and nitrate. weekly is recommend 5 - 10% so youre looking at about 5 gallons. did you cycle your tank before adding fish? also nitrate is the end of the nitrogen cycle, so that will keep happening (faster nitrate production) espcially in a smaller water volume environment __________________ “For most of history, man has had to fight nature to survive; in this century he is beginning to realize that, in order to survive, he must protect it.”― Jacques-Yves Cousteau MarineBio.org Current Tank Info: 40 Gallon Breeder w/ Bean Animal Overflow 20G Sump, Mixed Reef.

01/17/2015, 12:59 AM	#4
FraggledRock Registered Member Join Date: Dec 2014 Location: New York, New York Posts: 2,185	Probably around 25 -50 but try to reduce it asap __________________ “For most of history, man has had to fight nature to survive; in this century he is beginning to realize that, in order to survive, he must protect it.”― Jacques-Yves Cousteau MarineBio.org Current Tank Info: 40 Gallon Breeder w/ Bean Animal Overflow 20G Sump, Mixed Reef.

01/17/2015, 07:08 AM	#5
gone fishin Registered Member Join Date: Jul 2011 Location: Wyocena Wi Posts: 6,936	If it is a fish only I would not sweat the 15-25ppm of nitrate. If it got up to 50 or so then I would take more aggressive action. A lot of fish can tolerate very high levels of nitrate. I would guess you have in the neighborhood of 15-18 actual gallons of water. IMO you have a pretty good bioload in that tank, so nitrates could be an ongoing issue. __________________ Tony Current Tank Info: 180gal DT, BM NAC77 skimmer,3 Maxspect razors, Maxspect Gyre 150, 30g QT

01/17/2015, 12:55 AM	#3
cf17 Registered Member Join Date: Nov 2014 Location: Australia Posts: 26	Yes, I cycled the tank for a month before adding fish. How much nitrate is excessive?

01/17/2015, 08:55 AM	#6
dkeller_nc Registered Member Join Date: Mar 2013 Location: Central NC Posts: 5,062	As it turns out, water changes aren't a good way to handle nitrates on an on-going basis. Large one-time water changes are an effective way to immediately reduce the nitrate concentration in a hurry, however. A better way is with the utilization of an aggressive skimmer and carbon dosing. This article will get you started with what you need to know. I do this regularly in all of my tanks, even my 20g nano. I dose about 1.5 mL of vinegar daily when I feed the fish in this tank and nitrates remain undetectable.

01/18/2015, 04:44 PM	#7
cf17 Registered Member Join Date: Nov 2014 Location: Australia Posts: 26	Okay I will try vinegar and see how that works out. I was also thinking of getting some more live rock this week - would that help reduce nitrate?

01/18/2015, 04:52 PM	#8
dkeller_nc Registered Member Join Date: Mar 2013 Location: Central NC Posts: 5,062	No, at least not directly. The carbon dosing does two things - it encourages anaerobic denitrification bacteria in regions of your tank that are anoxic or at least low oxygen - that would include the bottom part of your sand-bed (if you have one), and the deep parts of porous live rock. It also encourages bacteria growth overall. Since bacteria require nitrogen and phosphorous to grow and reproduce, and your skimmer removes them from the tank, the effect is to reduce both nitrate and phosphorous from the water column.