The 5 in 1 dip stick tests are beginning to be real popular among fish keepers. It's inexpensive and easy to use. I always recommend that fish keepers have some means of keeping an eye on the water chemistry. You can tell a lot about the environment of the fish tank with the tests.
The water chemistry may or may not have had anything to do with the death of your fish. A good sign though is that your other fish are doing good.
You can clean off the algae, make a partial water change, and use an algae destroyer product to keep the algae under control.
The algae destroyer takes several days and may need more than one dose to completely kill the algae, so cleaning it off first would be the quick fix and the algae destroyer would stop the growth from reoccurring.
Also, if you have hard tap water, making partial water changes with tap water will not lower the Ph. You would need to use distilled or drinking water.
Please let me know if you have any further questions.
Kae
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