fish problems

Question
my molly after a couple of days could not swim right and when ever he went through our bubble decor he would just roll and couldnt not swim through it.  when the fish get to this point with no signs of other illnesses, what can i do to prevent death.  it makes me sad every time i lose a fish as i get so attached to them, and i just need your advice on how to prevent their early death


i have a 15 gallon tank with 8 fish and a pleco and it has been set up for 3-4 months now.  it has three black skirt tetras, two red platys, 2 dalmatian mollies, a white molly and a pleco



i took water sample to petco and they tested.  they said everyhting was fine but the ph balance was high due to the algae product i was treating my tank with.  which a different petco said that it would not affect my fish, so i am wondering if it did hurt my molly or not, although, the other fish seem perfectly fine.  also, the very next day my black skirt tetra was going onto its side and shaking and then returning to normal, but doing this like 2-3 times in a 5 minute period...so, i decided to test my own water and found that petco had lied to me as my ammonia was almost at a 1.0 and my nitrates were at there highest level that they should be which is 20.  i did a 20 percent water change right away, and my levels went down a little.  i am going to do another 10 percent water change tomorrow.  i cant get to my usual fish store to get medicine as i do not have a car, and we live 30 minutes from it and my fiance works during the day.  what else can i do to fix this problem.  i have also been putting a little of the aquarium salt in a little at a time as to not shock my fish.  any advice would be really helpful...please help me.  my levels have never been this high before and i dont know why petco lied to me like they did, and i dont want to lose my fish because of my inexperiance

Answer
Hi Rachel,
The first thing you should know is that those little test kits that people use are not very accurate, so it is very possible that either your kit is wrong, or the one they used at Petco is wrong, or more likely, both are wrong.  

 The best thing you can do is regular 25% water changes.  You need to do this at least once a week.  In your case, do it more often for the next little while to get things under control.

 Do not use algae control products.  They very likely can kill fish.  

 I see no reason to add salt to your tank.  Adding salt is one of those myths, which has little to no scientific backing.

-- Ron C.
  rcoleman@cichlidresearch.com
  Cichlid Research Home Page <http://cichlidresearch.com>