gravel in marine tank?

[Azure2010]

Hi,

I am setting up a FOWLR tank 55 gallon but I currently have it set up for African Cichlids with black gravel and crushed coral. I only have two baby Cichlids in this tank, so I am going to move them to my larger African Cichlid tank and convert the 55 g to marine but since it has a mix of black gravel and crushed coral, I am not sure I can use this substrate for a marine tank.

Is there any reason why I would have to pull this substrate out of the tank? I have only had it in the tank for ~2 weeks. Also, I have an undergravel filter in addition to a Marineland canister filter in this tank, so my next question is, can you use an undergravel filter in a marine tank if you also use sand and crushed coral?

I appreciate any advice you can offer and thanks for your help.

[mike_cmu04]

YOu will not want to use gravel or the undergravel filter because all the detrius will settle and you will have large nitrate problems that will not go away.

[theatrus]

I would not use a UGF in a marine tank (I never used them in fresh either) . The gravel could be used and may be beneficial for certain species tanks (mantis?). The problem is that the grain size is conductive to trapping waste and not great for most sandbed cleaning critters.

[crvz]

The problem is that the grain size is conductive to trapping waste and not great for most sandbed cleaning critters.

Agreed with this, which is a big reason why I don't care for undergravel filters either. Anything that is going to trap wastes is likely to cause nutrient related problems in the future (high nitrates, excessive algae growth, etc.). I would personally recommend getting a 1.0-2.0mm grain size sand in the tank and avoid gravel all together, while sticking to a bed depth of around 1-2" for ease of maintenance (I don't rely on my sandbed for biological filtration, simply for aesthetics in most cases).

[Paul B]

If you really want to keep that gravel you must use the UG filter in reverse.
Instead of having an air pump or powerhead pulling water up the UG filter tubes, you must push the water down the tubes. But this has to be done very slowly, the slower the better like 50 GPH. The water also has to be strained or filtered before it gets pushed under the gravel.
My reef has been running for 40 years like this so to answer your question, yes it can be done.
Good luck
Paul