Inherited sons aquarium

Question
QUESTION: My son has gone off to college and left me with a small freshwater (3 gal) tank, 5 neons, 1 black molly and 3 platys.  Several of the fish appear pregnant.  The tank has living plants (not too healthy) and a charcoal filter that pulls from the bottom and discharges at the top.  I know NOTHING about aquariums.  I am to feed the fish once a day......my only instructions.  HELP!!

ANSWER: Hi Laura,
Aquarium maintenance is very easy.  The only thing required to do is feed the fish and keep the water quality good.  Therefore, the only 3 things you need to do is, feed the fish, change out filter medias, and do weekly water changes.

Food, waste of fish, and live plant matter all decay and turn into toxic ammonia, which then is broken down into nitrite by beneficial bacteria, which is then FURTHER broken down into the least most toxic form of nitrogen, Nitrate.  The only way to remove nitrates is by doing water changes, which is why 15%-20% water change weekly is recommended.  Changing the filter all depends on how fast it is clogged.  Time can range anywhere from 2 weeks to 3 months.  

Remember that when adding new water, you must dechorinate it first.  Chlorine in tap water is very fatal for fish.  Water must be conditioned before adding.
-Let me know if you need me to clarify something else further-
-Matt-

---------- FOLLOW-UP ----------

QUESTION: Thank you!  I think I can handle that.  We have well water so chlorine
should not be a problem.  Do the plants need CO2 to make them healthy?  
They are breaking and look bad and the algae is taking over.  Remarkably
though, the fish look healthy.

Answer
CO2 all depends on the amount of watts given over the tank.  If the tank is recieving a lot of watts, algae will grow.  And CO2 will be needed to balance it out.  I also keep live plants and I remember when I did not inject CO2, I have 20 species of algae growing.  After introducing CO2, all my algae issues were resolved.  Only bad thing is, a CO2 system is quite expensive, it can be $300 for the regulator alone and $100 for the CO2 cylinder tank.  If you do not want to use CO2, you can just lower the light wattage and photoperiod of the lights.
-Matt-