Most fish will adjust to pH, it is the sudden changes from unstable pH that can be stressful even deadly. IMO/E the less chemical added the better, a good quality dechlorinator if on city water supply is the only chemical additive that you need IMO.
Freshwater fish need fresh water to thrive not just survive, over the years I have found that anytime my fish are acting odd.....a water change will fix it, however, if regular water changes have not been made the sudden change in nitrate and pH can make the fish sick or kill it.
To be a keeper of fish you must first be a keeper of water IMO/E
This is why IMO/E making regular weekly water changes are important for 5g and larger and twice weekly on 3g and smaller and understanding the science behind the water prams-ammonia, nitrite, nitrate, pH
I use both the API master kit and the strips and feel they are accurate, however, depending on what and why I am testing the API master kit is cheaper to use in the long run.
Understanding the nitrogen cycle is also important as well as understanding what the water prams mean and how they affect the fish, regardless of water pram reading the treatment is almost always the same....water change....the water pram test can help you know how much water to change and when in some cases.
Knowing that the biproduct of ammonia to nitrite then nitrate is the nitrogen cycle and know the effect of nitrate can help you safely make water changes.
We all know that ammonia and nitrite are bad...but did you know...
High nitrates can affect the immune response of fish, nitrate over 40ppm that is suddenly drop to 5ppm from a water changes can shock the fish often killing it if it was in a high nitrate water or when you add new fish from a low nitrate tank to a high nitrate tank the new fish gets sick and the old fish get sick from them due to their low immunity......ever hear someone say that a water change killed their fish or new fish caused all their establish fish to get sick or die...this is why....high nitrate.....fish will adjust to the slow rise in nitrate and live just fine...until......a large volume water change or new fish added.......
Same with pH, it is that sudden change in the pH that is harmful and the additives most often sold do not have the needed buffer to keep the pH stable and safe.
Remember fish shops are in it to make money so they want to sell you as much stuff as they can...the more fish that die the more money they make when you come back for more....just saying.......
Understanding the science so you can be proactive and educated will make this hobby so much more fun for both you and the fish.....
Freshwater fish need fresh water to thrive and live a long healthy life, anyone can have a fish but to be a keeper of fish you have to be a keeper of water and understand the science behind it...plus it is fun and easy........