Under Gravel Filter?

[Joeyg2100]

What is the minimum size of gravel that I could use, and still have my undergravel filter still work? I have some fine gravel that I want to use, but I think that it might be to small. It is soilmater select, which is the gravel substraigh that they put on baseball fields. It seems pretty fine, and I put some on top of my undergravel filter. It didn't go throught the grates, but it looks like it might not let any of the water/trash through the filter and let the filter work like it is suppose to. Please let me know

 

[TwoTankAmin]

A medium size gravel bed 3 inches deep is best for use with undergravel filters.

 

[woogrl]

I would assume that as long as the gravel didnt fall through the grate and you had the proper rotation of water through it then it wouldnt matter. The under gravel filter is not meant to pull large pieces of "trash" through it, it is meant to be a housing unit for benificial bacteria to grow and detoxify ammonia and nitrites. The water will be able to go through but if it does pull poo and other thing through how are you going to get them out? You dont want it to sit under there and continue to rot and decay because that will only cause other problems. If it gets too dirty under your undergravel filter you are probably not preforming enough/quality gravel vaccums or you are overfeeding. Just my 2 cents

 

[xJake]

A medium sized 3" bed of gravel will do nicely; however, I don't recommend undergravel filters at all. If you're looking for good biological filtration go with a sponge filter they're much easier to clean (simply squeeze out in a bucket of tank water) and you don't risk leaving a bunch of muck under the filter that will rot and decay and you will never be able to clean. I had been using one in my main tank (was what it came with and I didn't know any better) but I switched it out over the past month for 2 sponge filters on each end of the tank. So much detritus had built up underneath it that when I pulled it out the water turned almost black.

 

[Bignose]

I wrote this several months back, just an opinion on why I (and many others) have moved on to other forms of filtration than undergravel beds:

I think perhaps the real question is why do you want one? In almost every case a hang-on-back filter is better, especially one with a bio-wheel. The best thing about having the bio-wheel is that you know exactly where all your good bacteria are cultured, so so long as you take care of that wheel, you don't have to worry about re-cycling the tank.

There was a time that the undergravel filters were the best technology out there, but today that is just not true. Here are some of the drawbacks: the gravel bed, since water has to flow through the bed to be filtered, may develop channels, also known as ratholes, through the bed. This is bad since if the water is not running into the gravel too often, it is effectively getting not filtered. And that will happen since the water will take the path of least resistance, which is the rathole. Next, since the bacteria are under water, the water has to be well-oxygenated... the good bacteria need oxygen to work. With a bio-wheel, the bacteria are exposed right to the air, which gives them at least 1000 more oxygen to do their work with. Another thing I like about the biowheel filters is that you can immediately see if it is working correctly, that you can see is the flow rate of water is faster enough, you can see how often the wheel is spinning. And, again to fix this, you just take the wheel off, float it in the tank, and then clean out the filter itself. You know the bacteria are safe on the wheel, and you can clean that filter and pump and the filter pads and anything in the filter as much as you want without worry about a cycle. Comparatively, since with an undergravel filter the entire bed is the filter, you actually have a limit on how much you can clean the tank. Clean too much, and you may cause a mini-cycle. With the bio-wheel, so long as you match the pH, hardness, and temp of the new water with the tank water, you can actually do as large a water change and cleaning that you want. This could be good if an emergency arises.

Ultimately, you can never use sand with an undergravel filter, very few plants do well -- they don't appreciate the currents on the roots. And, there are just better, easier technology for use today.