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I've got an 6" Red Devil. It killed my 6" Oscars, a Wolf fish and 4 Catfish algae eaters a year ago. I know my 50 Gal. tank is big enought to handle territory issues, [color=green][i][b]however the  Devil will have noone in the Tank with it. Which brings me to the algae build-up. I Clean, keep the light-off[b]  and I seldom use flake-food and I still get an thick algae build-up every  2 weeks! Does anyone know what can I do to solve this and quit putting me though changes ? In other words...........HEELP!!!![b][i][/b]

Hi, Spiderly, and welcome to the forum!  Sounds like you have a couple of problems there -- the algae being one, and your Red Devil's territoriality being the other.  Actually, your 50-gallon tank is -- as  you've found out -- a war zone waiting to happen if you put anything else in there with the RD.  They need their space!  Once your RD gets his growth, you're going to have a lot of work keeping the water quality up to par.  The amount of bioload on that 50 gallon will necessitate almost daily water changes to keep up, even with careful feeding.  That leads to problem # 2 -- the algae.  Algae need two things to thrive -- light and nutrients.  Many times an algae problem is caused by the side(s) of your tank being exposed to direct sunlight, such as thru a window.  Is there a lot of ambient light in the room?  The other issue is feeding.  One of the toughest parts of keeping big cichlids is not letting them con you into overfeeding them (I've made a few trips to the rehab center for this myself!).  They don't need nearly as much food as they'd have you believe.  It's hard for me to know how much you're feeding him, but with that kind of algae problem, it's most likely too much.  At 6" your fish is still growing, so I'd continue to feed him once a day, mayve even twice, but relatively smalol amounts.  In nature, most predators don't know when they'll get their next meal, so they'll usually eat as much as they can hold.  Might be awhile before they can catch another meal!  Also in a large body of water, the waste products are carried away by the stream, diluted by the size of the lake or whatever, and metabolized by plants.  In an aquarium, food is delivered regularly, so they're likely to eat much more than is really good for them (just as some of us do).  At 6", my starting point for meals would be 2 large pellets served twice a day.  If he's still ravenous, give him another -- maybe even a 4th if he's still begging, but the next feeding be watchful, because his true hunger level will probably be somewhat less.  Don't assume each meal should be exactly the same amount.  Don't feed him till he's full -- just till the edge is off his appetite. 

I'm assuming you have adequate filtration, that is cleaned regularly.  I'd also suggest at least a 50% water change once a week.  If you're not doing that much, build up to it slowly, so as not to shock him with a sudden change in water chemistry.  I change mine
about 70% twice a week -- hoses are the way to go, not buckets, unless you just like working out! 

RD's are actually rather gregarious, sweet-tmepered fish -- if you give them a lot of room.  In anything less than around 350 gallons though, it's a different story!