what kind of filter?

probably depends on your maintenenace and how your keeping your tank.
 
It's probably not the problem, but what filter do you have(is it big enough for the tank)? What exactly do you mean by clean(you could be doing too much, that is as bad as not enough)? Are you overfeeding?
The bio-wheel is just a place for beneficial bacteria to live. It provides no more mechanical or chemical filtration than any other filter. It's main benefit is that when you replace the cartridges you don't remove all your bacteria. I would not put on another filter yet because it's probably something else.
 
Again with the filter suggestions. Everyone always asks this question and there is never an answer.

All of the major brand filters work about as good as each other. All that makes any difference is the flow rate, media types, and the way you yourself maintain the tank.
 
Which of your tanks are you talking about and what is your current set up?

The bio-wheel isn't going to make your water clearer. How you maintain your tank will be more in the play.
 
Your friend may have a lighter bio-load, feed less, and gravel vac more often. Most of us do Weekly water changes. You do Bi-Weekly.Maybe try doing weekly water changes for a month see if this helps. How is his water super clear and yours not? Is yours cloudy, greenish? The use of carbon can polish your water. Maybe he uses carbon or changes it more often than you. Good Luck.
 
In my Asian tank I hardly change my water once a month and it stays super clear. I personally think it's bioload and feeding as well as how many plants you have. My other tanks require the normal weekly or fortnightly water changes to stay beautiful as they have fewer plants.
 
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