pH level issue questions HELP!!

I am using aquarium salt, and the stuff to remove the clorine and metals from the tap water cant off hand think of what its called... I am not a brand new tank owner I have had a tank for prob 4 yrs now but those fish have always done great never any issues I upgraded them to a 120 gal because one is an Oscar and he was just out growing his 55gal, he is also roomed with a red fined shark, 2 Chinese algae eaters, 2 gold fish, 6 tetra, and a pleco. So I do know a lil about tanks. But for some reason when it comes to this type of fish I cant seem to keep them alive for anything! My pH tester is a good API tester where you put the water in the tube and put 3 drops in kind of tester. The little chart it comes with reads as high as 7.8 which is blue, and my water test right at that color, very blue! I agree I hate the test strips as well... I am just not educated well enough yet to know other types of prob that could go wrong I guess like the issue I am having. I just dont see a reason y they rnt staying alive.

You need to get the full API Master Test Kit (the liquid kind) and change the water whenenver you have any ammonia, any nitrites or nitrates over 20ppm. Without the test kit, I would be doing 50% water changes daily to protect the fish. Please stop using the aquarium salt, it is unnecessary.

Please either find a new home for your fish in the 120 gallon tank. Goldfish are coldwater fish and can't live with tropical tankmates, oscars are extremely aggressive and will eat all of those fish, especially the tetras. The pleco is a poop machine as is the oscar and the goldfish. This tank is likely not cycled either and I suggest you start doing 50% water changes a day on that one as well. It is very poorly stocked and you really need to rehome most of those fish.

If you want to keep the oscar -
1 Oscar
1 Pleco

If you want to stay tropical -
1 Red Tailed Shark
2 Chinese Algae Eaters
6 Tetra (You could up this school to around 30)

If you want to keep the goldfish -
2 Goldfish (your can add one more if it's a commet/shubunkin you can add four more if they are fancies)

you keep saying that but they have all lived with each other for 4 yrs and no one has killed anyone, except for the tetra they are the newest ones in the tank. I have 6 of them in there so then I am sticking with the right amount. My gold fish are 3 in long themselves. My temp is about 75... I would say out of all the fish the chinese are the most calm along with the shark... and they are prob 2.5 maybe 3 in long each... they have never hurt any of the fish including the tetra. My Oscar is not a normal Oscar he wont eat fish that y I have gold fish, the ONLY reason I didnt want gold fish as pets. So I have stopped putting feeders in there. When he was younger he ate them but as he grew he stopped wanting to eat fish and shrimp.

Now with my other tank, I am going to pick up the tester you all have recommended on Fri because our town doesnt have a very good pet store that carries that kind of stuff... I will start testing for what you have told me. The fish that have survived that water seem to be doing great but the tank has seem to have changed now. I dont have this strange whiteish film building up in my filter and tank any more like I had. So all seems well at this point so I will see what the tests say when I get it. So you say if the nitrates and nitrites are high the only way to fix it is every day water changes? Should have I have live plants is that the way to go?

Ok so you want numbers... Ammonia was 0, Nitrites was 0, and Nitrates by the color I am going to go with I think was 10 poss 20 but no higher than that for sure and the book says it shouldnt get any higher than 40.... You want to know the hardness results however I either dont have that good of a test or dont know how to test for it... LOL How do you test for hard water? Living in the city I do that is a large possibility!

Its so strange I am just not hearing about the salt! Every pet store around even our good lil local ones say you must have salt lol but I will stop adding it. I have always been told thats what helps them keep their healthy slim coat.

I have had my new fish a wk now everyone is acting great except i randomly lost one of my older fish that had been in there the longest the other night! He was acting just fine and I came home and he was dead! Doesnt make sense if my numbers are testing like you all say they should be. Its been almost 2 wks sense a water change and my water is down about an inch and a half from the top and even though my numbers are good I am doing a water change today!