This is getting off-topic but if @anewbie 's tapwater is low in sodium and potassium cations it could quite possibly be in the 120's ppm TDS and GH 7. Also depends what anions are present.1dGH = 17.8 ppm - something doesn't look quite right on your tap water TDS reading, GH 7 + KH 3 should be a fair bit higher than 120ppm TDS.
1dGH is equivalent to 17.8 ppm Calcium Carbonate but expressed as calcium is only about 7 mg/l (ppm). KH is only 3 so lots of wiggle room on the carbonate side of the equation.
@Conort2 love the tank!