Please note the corrected gallons figure, based on the dimensions you supplied. Kidney volume is always a bit of a guess, but the volume shown is for 90% of an enclosing 18x28 rectangle.

You didn't list your TA level, but you probably want to have your TA between 100 and 130 ppm, and your pH a bit lower.

But, the real key is making sure nothing grows -- if you get slime or algae growing, your chemistry will change, no matter what you set it at now.