Mollies died/ squiggly white very thin worms

Question
Okay so we had 2 fish 1 male Molly and 1 male Guorami and 2 snails; I know Gourami's are semi-aggressive but we read somewhere if you keep a few plants set up then he should be okay. He was okay, but the Molly was a little nervous looking, so we got 2 more Mollies (at separate times). We found out later they were females, of course 1 had babies so we separated them, but read if the tank has plants they could hide. Well the female who never got any love ate them...Well except the 3 hiding away that popped up weeks later. Just last week the black female died then the day after the Dalmatian female died. Before the black Molly died she looked a little lighter. Then the Dalmatian 1 always looked bloated (we just thought she was pregnant)she never had babies and we had her for like 5 months. Also... The male never wanted to mate with her. Do the males only like 1 out of so many and stick with them or does it sound like she was she sick?? The Guorami looks lighter mostly in his face he used to be much brighter! Male white Molly looks yellowish. Last question.. I just found a bunch of white skinny squiggly worms and I am freaked because I watched this video, and this guy had the same looking ones coming out of his face. I read these worms can not hurt the fish?? They can't live out of h20 right?
I know I am probably paranoid and this would not have happened if my daughter was here to clean out her own fish tank!I just need some piece of mind cause my skin's crawling with nerves "I HOPE JUST NERVES" Oh and we have a 2o gallon tank with a 30 gallon filter. How often are you to change the gravel?

Answer
Hi Jessica,
 The white worms are a dead giveaway about what is wrong with the tank.  You need to do more frequent water changes.  You should be changing 25% of the water once a week, every week, to keep the tank happy and healthy.  Do not put in any medication to kill the worms. That is the wrong approach.  You just need to clean the tank (i.e., change the water) more often.  When you change the water, you should use a gravel siphon to remove 25% of the water while cleaning the gravel at the same time.  That doesn't have to be exactly 25%, but I generally don't do more than 50% at once.  Then, replace that water with new water.  You never need to CHANGE the gravel.  

 Specifically, the worms indicate that there are too many nutrients in the water typically because of uneaten food and accumulated fish waste.  Changing the water will fix all that.  But, you should also make sure that you are not overfeeding the fish.  Give them only what they can eat right away.  Never give them food to "eat later".  It will only rot and foul the tank.

-- Ron C.
  rcoleman@cichlidresearch.com
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