tank maintanence

Question
I have 2 tanks, a 29 gal and a 55 gal.  the 29 always stays nice and crystal clear with minimal maint. it houses an angel fish, a few silver "shark like fish"  a small pleco and 2 snails.
My 55 gal is always a mess. it has an oscar (9" long) 2 silver dolars (4" diamater) and a sailfin pleco (10" long) The water is always turning green or slightly cloudy, the sides of the tank get a white scaly buildup on them that I have to scrap off every other week. the filter tubes get black on the insides, the rock are all covered in green algae.  
I've tried various "tricks" to keep it cleaner like growing live plants to compete for nutrients in the water to keep the algae down, (the oscar just detroyed and ate the plants)  feeding very lean, keeping the temp lowwer etc.
I have 2 filters on the tank rated for up to a 60 gallon tank each. the lights are on timers that go on 4 hours in the morning, off 1 hour in the afternoon and 4 more hours after that so they are only on 8 hours a day with a 1 hour window in the middle.
Is the tank simply overcrowded or could there be something else?  I'm on a 2nd floor apt. I'm worried about all the weight of a larger tank. (125 gal)


Answer
Dear Mark,
The simple answer to your problem is-- your 55 Gal is houses higher maintenance creatures than the much cleaner tank with the low bioload Angelfish and others. Oscar tanks need special care and actually, your 55 gallon is really overstocked. One mature Oscar is plenty for a 55gal, with no other fish. Oscars are simply too large to have to be crowded in something like a 55gal. In my experience, it is best to have one oscar alone in a 55gal. If his personality will allow it (not too aggressive or overly shy) a larger aquarium of 80 gallons and preferably at least 100 gals could house several other medium/large cichlids or a medium size catfish.

But the simple answer to your problem is your Oscar tank needs much more cleaning and maintenance. A setup like yours will need twice a week 50% water changes (including plenty of gravel vacummings) and lots of scrubbing with an algae scrubber to keep it nice and clean. Filters should be cleaned just as frequent.

When you own a oscar, you must make a strong commitment to their special care they need. LOTS of water changes, and much more maintenance than an average community fish setup.
I'm sorry to say your aquarium is quite overcrowded especially with a 10 inch sailfin pleco. These big guys are high bioload creatures. Lots of water changes solve or hopefully help a little with this problem.

(Sorry if this wasn't what you wanted hear, but i'm only speaking from experience)

Remember when doing water changes to always make the replacement water equal in temperature to that of your aquarium and properly dechlorinate it with a good water conditioner.

{I noticed you mentioned you're worried about all the weight of a 125gal aquarium. Well, unfortunately I do not have much experience with these kinds of things. I think you may be better off contacting the apartment owner and asking if he/she knows if the floors are supported enough to hold the 125gal's weight of an estimated weight of 1,250lbs or more.{

I really hope this helps!
My very best wishes and happy fishkeeping!
Karen~