Fertilizing rainwater

[malteseproverb]

I've finally achieved my dream of having a rain barrel (yay) but now I'm wondering if I should be altering my fertilizing regimen in any way now that I'm using rainwater. I normally don't fuss over fertilizer: my approach has been to fertilize as little as possible and avoid it altogether if I'm lazy, but that was an attitude borne from dealing with somewhat hard tap water. Now that I'm going through the trouble of hauling gallons of rainwater from my yard to my tub on the second floor, I want to make sure I'm not missing anything here.

Here is my current fert schedule:
1/8 teaspoon Dyna Gro (7-8-6) + 1oz liquid kelp (0-0-1) once per week. I water twice per week for most of my plants now that it's summer so generally speaking I fertilize every other time I water (disregarding my mounts which are watered every day). According to Ray's TDS calculator I'm using about 12 ppm N and around 30 ppm TDS. I drop the kelp in August/Sept and I barely fertilize at all in winter, maybe once a month.

I'm worried about the amount of calcium I'm providing now that I've shirked my tap. Dyna Gro has 2% Ca and 0.5% Mg but I'm using it at 1/4 the strength recommended on the label. Should I use a Cal-Mag supplement? Should I purchase a fert that's formulated for rainwater? Is ph even something to worry about??

Maybe there is no right answer but let me know if anything leaps out at you as a bad practice. Thanks!