all my fish keep dying!!

Question
hello! i hope you are well and i hope you can help me.... i have a ten gallon tank with a filter, heater, gravel, lots of fake plants and 2 stone "hiding place" i started out with a goldfish a sucker fish and a red platty wagon then i got two moores. i then moved to a new house and things went down hill from there. the moores bred and only one baby survived the gold fish turned white over a week then died the red wagon died then the mollies dies all with in 2 months. i started noticing white lines on my sucker fish but he seemed to be ok and acting normally. so i cleaned out the tank and i got 2 angel fish one died within a week and the other did great grew bigger and everything. then i had to move again.....i wanted more fish so i got 2 mollies and they both died within 3 days and then my angel fish got sick his head swelled up and he had red dots on top and he couldnt close his mouth and didnt swim much then he died yesterday. i dont know what to do or why all my fish keep dying so now i only have a baby moore and a sucker fish ive been doing resurch and i think from how it looks the sucker fish has ick. should i prepare two new tanks and seperate the fish and treat them? how should i treat them how do i find out whats really wrong with them and what do i do with my original 10 gallon tank what should i save and what should i get rid of is there hope for me to save my 2 surviving fish and ever having angel fish and school fish again??? please help!!! Thank you!

Answer
Hello,
You must cycle a tank before adding fish.  To cycle a tank, you must buy a used sponge from your pet store, and put it into your filter.  A used sponge is full of good bacteria that fish need to survive.  Squeeze out the access water, and put the sponge in your filter.  Never rinse a sponge under tap water.  When cleaning your filter, always rinse the sponge in water that you have removed from your tank.  Let your water run with no fish in it for about three weeks, adding water that has evaporated from your tank.  Check your water after this time.  Your water should have zero ammonia, zero nitrites, and nitrates must be low.  Ammonia, and Nitrites are the number one killer of fish.
Always make sure the fish you buy have the right PH, temperature, and that they will get along.  Goldfish do not mix with tropical fish.  Angel fish do not mix with Mollies.  Angel fish need 10 gallons of water each to be healthy, and happy.  They need acidic to neutral water.  The tank must be heated to 80 degrees.  Mollies live in salty, alkaline water, there pH should be 7.6 -8.0 You must add 1 teaspoon of diluted aquarium salt to 2 gallons of water.  Mollies need more salt than other fish.  
It is very important, before you by fish to read up on them.  Not all fish live in the same water, not all fish get along.  Never overstock your tank.  This is a big mistake that many people make.  Fish need space to swim.  A 10 gallon tank is too small for 2 Angel fish.  You would have room for 6 mollies, and this would be your limit.
Goldfish, and platies do not mix.  Goldfish also need big tanks.
Your problem now is to cycle your tank, then choose fish that will be happy in your tank.  If you do not want to go with mollies, there are many other little fish that would be happy in your tank.
Once your water chemistry is right, do 25% water changes every week.  Do not add all the fish at once, because it would change your water chemistry killing them all.  Buy two fish, wait one week, do a 25% water change, check your ammonia, and nitrites.   If your water chemistry is right, add two more, wait one week ...and so on.
I hope this will help.
Lynda