It is not so simple as just adding things up. The GH test for example compares the things it is testing to calcium carbonate. http://en.wikipedia.org/wiki/DGH
Similarly the Ca and Mg tests may not report Ca and Mg, but some other equivilant. (Sorry for being so vague, it has been a while since I have looked into these details) http://www.thekrib.com/Plants/CO2/ha...arryfrank.html
My tap water is just under 300 ppm per my TDS meter, and my soft water fish that were hatchery raised are OK, including Discus, but I need RO for German Blue Rams.
GH and KH are around 4-5 German degrees of hardness, and these do not add up to 300 ppm, either, but under 200 ppm, even on a day when both are reading 5 degrees.
My hard water tanks (Lake Tanganyika) has a TDS closer to 800 ppm. My Brackish water tank (SG 1.004) has a TDS of about 2000 ppm.
I would call your water fairly soft, fine for hatchery raised soft water fish, but look into RO for the most delicate fish, and for breeding soft water species.