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Changing Aquarium Filters

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I currently have two of the large coop sponge filters running in my 55 gallon community tank.  Have a mix of species, guppies, panda corys, hillstream loaches, cherry shrimp, and four otos.  I have a fluval HOB filter running as well that I added to clean up the water a bit.  I am looking to remove the HOB filter, but I am worried about losing bacteria.  It has not been running the entire time the aquarium has been setup(we are going into year 3 of the tank being up).  If I remove the HOB filter am I going to crash the tank??

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Hey @Dakotascott71. My personal belief is that you should be able to remove the HOB without issue. You’ll definitely lose some bacteria, but it’s not like you’d lose it all as your other filters hold bacteria, the glass, your substrate, decorations, wood, etc. all hold bacteria. 

Me personally, I would remove the HOB, and feed a little lighter for like a week, and then slowly increase to previous feeding levels to allow the bacteria to replicate and replace the minimal amount that will be lost by removing the HOB 

Edited by AllFishNoBrakes
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On 1/14/2023 at 4:34 PM, Dakotascott71 said:

I have a fluval HOB filter running as well that I added to clean up the water a bit.  I am looking to remove the HOB filter, but I am worried about losing bacteria.

I actually did this on my 29G. Running 2x large ACO sponge and then running a HoB for the sake of polishing the water (seachem tidal 35).

Basically my method is to take the ceramic media and set that in the tank on top of the sponge filter. That helps to keep the bacteria in the water. Not mandatory, but it helps.

I actually did that process a few times. I had issues swapping lids which meant the filter was in and out of the tank for a little bit. I ended up having to move the tank 3x as well due to a variety of random household issues. 😞


The tank cycle is generally fine with the above method.  What happens if you just pull the filter? As long as bioload doesn't change you should be fine. In my case on this most recent removal (filter and media removed) I did have a very small bioload increase and I've been dealing with cloudy water for two months since then.

Not a massive issue, just an annoyance. Why? Well. Those sponges have had a few "bacteria in a bottle" solutions, lava rock in the tank, and there's basically no reason for it to not have a cycle. The cycle is fine. It's just cloudy from the sponge porosity and texture.  I can pretty much guarantee, if I add on that HoB for a few hours, water will clear up and after 24 it'll be very clear.

I have used other sponge filters, they have a different texture to the sponge and different porosity with their own pro and cons.

Hopefully that helps.

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If you are solely worried about losing the beneficial bacteria, you will be fine. Those two sponge filters will handle the load fine. If the sponge filters have been in longer than the HOB, it is likely they have more bacteria in them than the HOB anyway. 

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I’ve been in this situation before. What I did was run 1 of the sponges for 30 days with the new HOB. Feed light for a week, and bump up slowly. After 30 days, you could remove the sponge, but I always kept it for oxygenation. There was another time, I ran out of coarse sponge pads so I cut up the second sponge filter to fit the HOB. Not the best idea because you sacrifice a sponge filter, but if you ran out of pads and already have a running sponge filter then…

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