Amar Salvi has been a nature aquarium enthusiast for over 35 years and owns his own Nature Aquarium Gallery in Navi Mumbai, India.
Can I Put a New Filter in My Fish Tank?
Many novice aquarium enthusiasts are in a hurry to do away with their old existing filters when they upgrade themselves to that new filter they always wanted. In their eagerness to have the new filter installed and running, they miss out on one critical thing.
What's that? Well, they threw out the baby with the bathwater (not literally). What they did miss out on was all the crucial nitro-bacteria that had colonized in the old filter media were thrown out, and the new filter with its brand new filter media was installed instead.
So, what you get is crystal clear water and some days later some fish floating upside down—dead. What went wrong over here? Well, you crashed the ammonia cycle, that's what happened.
The old filter was in fact the heart of the aquarium ecosystem, with all the nitro-bacteria in it, breaking down the ammonia, converting nitrite to nitrates. So when that 'old' filter was removed, the most useful part of the ecosystem was removed with it, and the ammonia cycle went out of control in just a few days with almost no bacteria to break down the ammonia build-up, so the ammonia and nitrite levels peaked, leading to fatalities.
So, how does one avoid this? Simple.
How to Add a Filter to an Established Tank
- Remove the existing filter media (sponge, ceramic rings, etc.) from the existing filter.
- Place some part of it along with the new filter media to help colonize the new filter.
- Let both filters run in parallel for at least one week before you remove the old filter.
This gives the bacteria enough time to colonize in the new filter. So, that's why you shouldn't throw out your old filter when you get a new one!
Questions & Answers
Question: Can I feed fish as usual when transitioning from old to new filter?
Answer: Yes, of course. However, keep feeding to only as much as the fish can finish it all off. There shouldn't be any leftover food, which will decay and cause an ammonia spike. Feed away from the outflow in a relatively steady section with low flow so that the food is not carried away in to difficult to reach areas.
Question: Oh we've totally messed up. We've just taken the old filter out and put the new one in. Now fish seem sick. We took the old filter out 5 days ago, still got it, is it too late to put it back in and run it alongside? Or what else can I do? I have started adding a bit of filter boost. My poor goldfish..
Answer: You haven’t described what exactly is the issue you are facing with your goldfish. Is it panting too much (as in gasping) or has it kind of settled itself down and not moving much. Check if the air supply is functioning well and turn it up as much as you can. Secondly, do a water change, at least 50%, but ensure that the water is de-chlorinated first and is at the same temperature as the aquarium water. You can still use the old filter in parallel, as long as the media in it is still wet, as the bacteria will still survive partially in those conditions, but I wouldn’t recommend that now. Water changes will remove any ammonia traces, till the new filter settles. Add a de-nitrifying bacteria culture if available.
© 2012 Amar Salvi
Read More From Pethelpful
Underwater adventures on June 12, 2020:
Very useful site. I was going to leave.my new.filter.in for six weeks. So after what you've said I maybe overdoing it .
One week enough eh? So for shrimps..this still applies?
I changed over from Interpet' CF2 TO EHEIM pickup160
Reason...shrimps getting into CF2 and munched up.
Will on February 02, 2019:
This is solid information thank you
the newbie on August 17, 2016:
So what do you do if you are changing filters because the old one is broken? Am I out of luck because I can not run them simultaneously?
Amar Salvi (author) from India on May 28, 2014:
Also,remember that the UV filter is actually meant to kill all bacteria, so its important that you add some 'muck' or part of the old media in to the new one to 'kick-start' the new filter.
TropiCo Aqua on May 25, 2014:
Run both filters in parallel for a week. That will help the bacteria colonize the new filter, you can move on to the new filter completely after about 10 days.
Angelo on May 24, 2014:
I'm upgrading filter systems from Aqueon Quiet Flow filter system to a Aquatop UV filter system. This is a significant upgrade. How can I switch out without harming the fish? Thank you
Amar Salvi (author) from India on January 28, 2012:
Yup,mate! Thanks for dropping by.Glad to see you have signed up. Will be posting about my experiences breeding tropical fish soon.
Sai Sandeep on January 28, 2012:
I really like science. i am the guy who frequently posts on ur wall in facebook.
Amar Salvi (author) from India on January 17, 2012:
@sweeaun...thanks for the feedback.Couldn't agree more.I am amazed at the number of budding hobbyists who continue to learn this the hard way,literally taking the tank to the cleaners only to have a squeaky clean aquarium...and a few fish upside down.The more we let an aquarium mature,the more stable it will be.
sweeaun from Malaysia on January 16, 2012:
Good post. Everyone should get educated on nitrogen cycles before embarking on this hobby. We'll have less fish fatality then.