Hi welcome to the forum and the hobby
Unfortunately you have gotten off to a bit of a bad start but its not your fault its the shop. First thing I would do is stop using the ph product they are notoriously bad as they are hard to keep stable in the long term you are better off finding fish that are well suited to your tap water.
Second thing to do is have a read of this section of the forum
http
/www.fishforums.net/index.php?/topic/277264-beginners-resource-center/
The beginners resource section, loads of great articles in there. The two most important ones for you to read are the Nitrogen Cycle and the Fish In Cycle. You could also read the fishless cycle as it is not too late to start that, should you be able to rehome your Tiger Barbs. Fishless is a lot easier to do and a lot safer for the fish but a well controlled fish in cycle is okay but its hard work especially on a tank this size as it involves daily water changes.
The problem with the way the store has suggested you start off is your filter has been sat with no source of ammonia which is what it needs to support the on going cycle when you have fish. Ammonia is a by product of any rotting organic material - in this case the largest part of this is fish poop. The problem is though Ammonia is toxic to fish so you need the bacteria in your filter, none of the off the shelf products really work, there are claims some do but for me the best thing to do is provide a source of ammonia and wait. In the fishless cycle you do this with house hold ammonia in concerntrated amounts each day for about 5 weeks then add your fish.
For me I really would think about taking your fish out, the store will dismiss this as nonsense but trust me 90% of the shops in the world will say the same as they are not going to make money off you by selling you fish in the early stages while they are all dying and the products you need are not really working. The only products you really need are liquid test kits rather than the paper strip ones and a good dechlorniator for water changes. The reason I say start again wth a fishless cycle is, my tank is a little bigger than yours at 135 gallons and if someone told me large daily water changes or rehome your first 5 fish it just seems a bit simple for what to do...
The other good thing about this is it gives you time to think about what fish you really want as a trip to the fish shop often only shows 10% of the fish available and the worst thing is getting a full tank and then realising you love a certain species and you cant get it....
Sorry if its all a bit daunting but most people get into this situation.
Wills
