Hi, everyone.

First time poster and aquarium newbie here. Please excuse me and let me know if I did anything wrong regarding the forum rules here.

I have a clear bottom tank for goldfish. In my current setup, I have an underwater powerhead attached to a sponge filter. My sponge is getting very gross, like slimy and breaking into pieces. Routine cleaning of the sponge gives me goosebumps.

I am thinking about filling the filter canister with gravel instead of a sponge refill. Is it a good idea? My thinking is as follows:

When the power head pumps water thru the canister, the water passes over the gravel to form a biological filter. Will this create an equivalence of my original sponge filter? If not, what are the major differences and pros and cons of each approach?

First off
The down sides i see to using gravel in the canister is that you are not going to catch any real small debris like you do with the sponge filter, also I do believe you will get a much larger surface area with the sponge allowing you to have a larger colony of beneficial bacteria.

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use lava rock.

or replace the sponge.
I do suggest tho you get some sort of prefilter or the lava rock will clog up.

Will lava rock change the pH of the water?

Ceramic rings would do the best job and provide a larger surface area than either the sponge or the gravel with the inner diameter being open or bio-balls better yet and they are made for just that purpose. They are not hard to clean and they also hold up better than the sponge.

Rose

lava rock is inert. so it will not alter water chemistry.
bio rings are better but cost more.
lava rock is porous and works well. a sponge prefilter will help if using either one. as it will help toreduce detritus build up.

do you guys thing that sand might work better?

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I'd vote for ceramic rings all the way. I've been using them in my canister filter for the last 10 years and have no complaints.

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When in doubt, do a water change.

I don't think sand is a good choice because it will slow down the water flow or even clog the powerhead. I'll use lava rock for now because I found a bag of lava rocks in my shed. Thanks all for the ceramic rings suggestion. I'll keep that in mind when I shop for supply next time.