I use Tetra Tetratest Laborett for my testing kit. I believe I bought it for $25-$30 dollars. Avoid ALL test strips. They are inefficient and are a waste of money.
As for gH and kH. My tank goes anywhere from 4-6 gH, I made sure my water parameters were roughly the same as DK's when I received my first 2 units of BTs from her. My kH is consistently 6, but I know DK's is at like 0-2. My BTs don't seem to have an issue with this.
My pH is now always 6.5 due to my diy co2 and I don't have issues with it getting higher then 7.0.
So for me, gH of 4-6, kH of 7, and pH of 6.5 is my target. My BTs are happy as can be, expect when I had a mishap a few weeks ago and accidentally co2 poisoning 4 to death (Accidentally kicked the powercord out of my powerhead to make surface agitation). But to me, BTs require upkeep. You can't get lazy with the tank you are housing them in. They are easier to kill.
OK, I'm getting lots of questions on the BTs, so here goes:
Tank conditions that I keep them at are essentially the same as for crystals, mostly because that is my native water type. They have been kept and bred in far different conditions by the Germans, who have totally different water than I do. However, it took me the better part of a year to transition them from my German import stock in their water to my water.
They are currently in pH 6.6, GH 2-3 KH 2-3 temp 70F, low TDS - I don't have a number for TDS but my well water comes out of the ground nearly like distilled water, and I put cuttle bones and some ground coral into the tanks to mineralize it a bit, but the water is low in salts. I keep them in tanks with turface as substrate.
The leaves I use for culture are predominantly dried white and red oak leaves, but I've used pin oak, beech, or maple leaves, too. Please keep in mind that my production tanks are relatively sophisticated, with fresh water infusions twice daily.
In those latest pictures they are eating boiled beet leaves, just because that's what I have growing, now. They also eat spinach, dandelion, broccoli, snow pea, etc. They seem to like anything green, but not colored so much such as carrots, etc. They also love squash - zucchini. And I feed them Hikari sinking wafers or generic old flake food.