Your tank seems to be carry a lot of fish in it i would suggest getting rid of the plecos because they poop a lot witch can cause a spike in ammonia, I had the same problem but with goldfish with two mollies that i still have and they are super hardy. You should buy some ammonia remover like this Fluval Ammonia Remover Replacement Packs at PETCO
. It is for another filter but i just put it in the filter i had.
I thought that I was not meant to have fish either but things end up working out once you have the info you need. I have over stocked my self, I have treated for ich also and not all the fish make it, i treated two swordtails and the male died but the female made it and she is realy healthy. It WILL take about a week before you can "cure" ich, usualy the fish get it from stress and if you are adding chemicals in the tank like crazy of course they will stress out if you think it is the ammonia then do a 100 percent water change and scub down the tank with HOT water, that is what I did with my mollies. Look up if your fish are hardy and if some are not then keep them in a diff tank and put the hardy ones in the 30 and let it sit for a day then add the other fish but don't be discuraged if they just sit in the bottom of the tank for a while they will do that from the diff of the water put the Ich treatment in the tank as directed and wait a week, do not expect to have all the fish make it just hope they do. If the tank gets foggy then just let it sit there for a week do a cuple of water changes of 10 percent a day or two and let the tank alone and before you know it the tank is clean again. BEFORE you add the ich treatment remove the carbon form the tank so that the treatment wont just be removed.
AND SOME GRATE ADVICE I GOT FROM THIS SITE WAS NOT TO FEED THE FISH TOO MUCH, IT IS HARD TO STARVE A FISH JUST PUT WHAT THEY EAT IN THE FIRST 3 MINUTES. I had over feeded my fish before and that is a big factor when it comes to ammonia.
As for the ph problem, if you do a 100 percent water change and let it sit for a day or more then the ph levels of with the "cycle fish" and the other fish will be good. I have never had problems with the ph level because it is hard to change the level of ph, for me.