With the API tests, the number of drops for both GH and KH give the value in dH. So your GH is 11 dH and your KH is 12 dH. The conversion factor of 17.9 is for both GH and KH to convert from dH to ppm.
GH and KH ranges in fish profiles are given in either dH or ppm and your 11 dH for GH converts to 197 ppm and 12 dH for KH converts to 215 ppm.
GH is the most important parameter for fish. KH is only important to stabilise pH so doesn't impact fish directly. pH is also important but it can be outside a species' range provided GH is well within it.
The table in the instructions is a rather inaccurate list of fish they think can be kept at certain hardness levels (inaccurate as, for example, they say livebearers need 100 to 200 ppm but they actually need over 200 ppm with some species needing over 250 ppm; and the table might lead some to think that marine fish just need hard water not salt water!) Ignore this table, and look up fish on a reliable website to see what the hardness range for any species is. Fish should be kept in water with a hardness around the middle of their range.
Your tap water hardness is too hard for those species which need very soft water but too soft for hard water fish. However there are species which will do fine at your hardness.
But if you want to keep fish which need softer water than your tap water, you will need to mix your tap water with RO. The amount will depend on which fish.
It is possible that using RO to reduce GH will have no effect on pH; ignore the pH level and go by GH.
If you tell us which fish you want to keep, we can tell you if you need to use RO water or whether they would be OK in your tap water.