30 Gallon Tank - Gravel Filter

Hello,

I have a 30 gallon tank with various sized rocks and glass (no gravel). Under it I have a gravel filter that connects to two tubes where air bubbles up the dirt. Looking under the aquarium today I noticed two things. One I have a baby fish who was born there and trapped (he/she is free now) and a TON of dirt. The aquarium store (which has given me bad advice MANY times before) told me I don't need the gravel filter on a 30 gallon tank. Just get rid of it and use the water siphon to clean the dirt periodically.

Fresh water tank, about 6 plants. The water always checks out perfectly in balance (using aquarium strips).

Is this sound advice?
Pic of tank below

 

That undergravel filter will not operate properly with the large size rocks you have. It is also how your baby fish was able to easily get under it.

This is a valid filter with huge biological filtration capability but if you wish to use it you'll need to change to a smaller size gravel. 3-6mm sized gravel is best. If you do this you can still have some of your larger rocks on top of the standard gravel.

 

Ah. Why does it not work with large rocks on top? Is this due to lack of suction? I could probably switch to regular gravel at some point and use less rocks. I presume the process is

1. remove fish/snails and put them in container of purified water
2. remove all plants (put them in water)
3. Remove all toys
4. Remove the rocks, water
5. Replace water entirely with purified water
6. Replace gravel filter, add gravel, and put on rocks (less than before)
7. Replace toys and fish

 

It is designed to pull water through the entire gravel bed where the beneficial bacteria will convert ammonia to nitrates. This biological filtration is the most important type of filtration in an aquarium. Without gravel it will only pull water up from near the uplift tube, and there will be almost no surface area for the BB to grow properly.

Your plan for adding gravel is correct. But I would save and reuse about half of your present water, and then finish off with fresh, dechlorinated water. You'll need about 30 pounds of gravel.

 

I’ve never used an under gravel filter but from what I’ve read they can offer absolutely huge amounts of surface area if used properly, even better then high end canister filters, I think the trick with the under gravel filter is not too clean the substrate too often to allow bacteria to grow and maintain. As someone has already pointed out you’d need a much smaller gravel, also from your photo it looks like your running some find of powerhead or internal filter anyways in the top left corner? If your running a pump anyways you could always super charge the UG filter with a water pump instead of an air pump and make it more efficient. I’m using a fine sand substrate at the moment but next project I’d love to use an under gravel filter.

 

I have a bio filter on the top and it helps keep the water very clean. The air pump is rated for 50 gallon tank and split between the bubbler and the UG filter.

Today I will buy 30 pounds of gravel and redo the tank tonight

You guys have helped a lot. I appreciated it

 

Hello All,

I did the transfer Satuday night and it went flawlessly. I kept a few of the rocks (next to castle) , but pretty much all gravel. I'll be looking to buy a blacklight for the gravel at night. Added 4 new fish, found one of my dead snails (from the summer) - but no casualties and the water test strip is awesome.

Thanks a lot!