Can you Help me With this chemistry question involving pH and concentration?

When the PH= 7 the [H3O]= 1.0 x 10^-7. To know if that water is healthy enough I would assume acidity would be poisionous to fish. So I am guessing that anything below 7 is dealy to a fish due to the acidity and everything above 7 would be okay because it is basic.

Well first lets start with how you get pH of 8 from a hydronium concentration of 1.0*10^-8
we  know that pH is calculated by:
pH = -log[H+] where [H+] is the concentration of hydrogen ions in solution

We also know water is H2O while hydronium is H3O+.So this tell us that for every mole of hydronium we have 1 mole of H+ since H20 + H+ = H3O+
using equation we get: pH = -log(1.0*10^-8) = -1(-8) = 8
now use the same equation with a pH of 7 and solve for [H+]:

7 = -log[H+]
10^-7 = [H+]
So the hydronium concentration when pH is 7 would be 1.0*10^-7 mol/L

Since pH of 7 is neither acidic or basic it would be ideal for most fish.