Fish rubbing themselves

Question
The tank was setup in September of last year. I did a 25% water change in January (about 14 gallons). We use two kind of filter system, underdrain filter system for 55 gallons and tank glass mounted filter. Filter was cleaned on the glass mounted one at least monthly or two. We have not replaced the water other than adding fresh water to replaced evaporated water (usually a gallon a week)
We also never cleaned the bottom of the tank because we have bottom feeders. FYI - the water was very light greenish in color.
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Followup To
Question -
Hi Chris
I have a 55 gallons fish tanks filled with well water and the water was tested satisfactorily safe. Water temperature usually range in the low 70's. One thing the test reported was that it reported as hard water.
We have 4 danios, 5 guppys, 2 plecos, 1 cory catfish, 1 swordtail, and 2 platies.
We've lost one guppy who died from a bacterial infections (pop out eyes and protrude lip) and i've seen several fishes rubbing themselves against rocks or objects over the past month. I added stress coat treatment to the water as recommended by the pet store; however; several guppies gotten sick soon afterward and died after the treatment. Other fishes still live in spite of the the treatment. What steps do I need to do to help the fish rid of the irritation or something causing them to rub themselves? Thanks.
Answer -
Hi David;

If I could get a bit more info from you;

How long has the tank been set up?
When was the last water change?
How much water was replaced?
What kind of filtration?

Let me know as soon as you can.......

Chris Robbins

Answer
Hi David;

Your poor fish definately need some water changes and gravel vacuumings. All tanks need a 25% water change every week. The gravel needs to be vacuumed every 2 to 3 weeks. The bottom feeders do not benefit from waste being left in the gravel. It is harmful to them as it rots and all the fish will exhibit symptoms of irritation like the scratching you have seen. Adding water for evaporation is not the same thing. Water has to be siphoned out and the muck removed. An important thing to know is that in a tank that has not had a water change for awhile, you don't want to change more than 25% at a time. The tank water has developed such a different chemistry after several months, a bigger change could shock and/or kill your fish.

If you take a sample of water to the fish store, have them test the levels of pH, ammonia, nitrite and nitrate. Get the actual numbers of the levels, not just "okay" or "not okay". You need to know if your water changing efforts are showing, and future test results will reflect your progress and whether extra water changes are needed.

Here is more on the importance of water changes and how to do them;

http://www.indiapets.biz/fishes/articles/faf02.htm
http://www.aquahobby.com/articles/e_waterchange.php
http://www.aquarticles.com/articles/management/greco_water%20changes.html
http://faq.thekrib.com/begin-changes.html

At Your Service;
Chris Robbins