oscar fish not growing

Question
hello,
i was wondering if you could help me with some questions i have in regards to my fish not growing and my cloudy water in my tank.  i have a 55 gallon tank with two oscars in it they are still rather small i bought them at the same time and at the same store and they were the same size but one of them are not growing.the fish is normally active and does not seem like anything is wrong i had a scare one night she did not want to eat and all she did was sit at the bottom of the tank and it seems like the other oscar was helping her out she would not swim until the other oscar "pushed" her along but this only happened once in the 2-3 months i have had the fish. i just dont want her to be diseased and the other fish get sick as well. what can i do?  i also have an algae eater in the tank as well.  i have a hanging filtration system and i have had the tank up and running for a month now. i also got the water tested last week and was told i was at the stage where i have a nitrate spike and other than that the water is perfect.  i learned that one of the things i was doing wrong was washing  my filter out with tap water i havent done that with this tank tho, but the guy at the pet store said that by the tank being new that i should put some bacteria on the filter pad and that would help with the cloudiness but it may take some time. like 7-10 days but it is nearing the time and i dont see any change.  
hopefully this is enough info and thank you for your help.

Answer
Hi Erica,

The 55 gallon tank should be considered temporary because two oscars will eventually need 75+ gallons.  Some plecos get to be 24 inches and need a 100+ gallon tank.  

I would also consider upgrading your filtration system as soon as possible (oscars are very messy, like goldfish) to either a canister filtration system as they are the best or at least a filtration system that handles a 100+ gallon tank.  If you like hang on filters Hagen's Aqua Clears are great.  They make a 60-110 gallon version and it does not use disposable cartridges so you'll never spend another dime again on disposable media.  Plus, these hang ons are better because they host the beneficial bacteria in ceramic media.  When you toss out a cartridge you are throwing away beneficial bacteria that eats harmful ammonia and nitrites in your tank that are toxic to fish.  It never hurts to over-filter a heavy bodied fish tank.  This will help tremendously with the bioload and with the cloudy water and nitrate conditions.  If upgrading your filter simply isn't possible, at least buy the Hagen Aqua Clear biomax insert (looks like a mesh bag with white rocks) and put it in your filter so that when you do throw out cartridges you don't throw out all of your good bacteria as the media will save this.  

You never, ever want to rinse anything that you use for your tank in plain tap water, this destroys all the beneficial bacteria and can throw your tank into the re-cycling process and this can cause the fish to get stressed, diseased and even die.  

I'm sure the guy at the pet store did want to sell you some fake beneficial bacteria products to douse your filters pads in.  It's more money for them.  The truth is that these are a waste of money and shelf bacteria products simply don't work.  The best thing to do is to cycle a tank before you add the fish.  If you have no ammonia and no nitrites and some nitrates then your tank is cycled and you have all the bacteria that you need.  

You should not have cloudy water in a cycled tank.  I'm wondering if they meant to tell you that you had a nitrIte spike and not nitrAtes.  This would mean that the tank is still cycling and in this case you should be doing daily 25% water changes and double dosing the Seachem's Prime until your nitrites are 0, otherwise your fish will get stressed, ill and eventually could die.  Cloudy water in a cycled tank is from overfeeding and excess phosphates and will eventually lead to an bad algae problem.

If they really did mean nitrAtes, then this means your tank is cycled but your filtration system is not sufficient and/or that you are overfeeding or under-performing in routine maintenance.  You should still do 25% daily water changes and syphon your gravel well until your nitrates are 5-20 ppm.  You should only have to do routine maintenance on a cycled tank once a month, provided the filter is excellent.  

You really need to get a liquid drop test kit and monitor these ammonia, nitrite and nitrates yourself.  The pet stores use generic, inaccurate strips and rarely ever tell you the actual number other than it's high or low, followed with bad advice on how to correct it.

I wouldn't worry if you've only had the oscars a few months and one is bigger than the other.  Females versus males can be quite different in size, even for the same age and same diet.  I bought two orandas at the same time that were the same size but a year later one is markedly bigger than the other.  They have been in the same tank and have eaten the same food and are the same age and were purchased at the same time but one is a female and one is a male.  My female oranda will always be smaller than my male.

Good luck : ) April M.