dosing ferts and dealing with cyanobacteria

Yes, there are test kits for Nitrate, Phosphate, and as you already know, you can determine the CO2 concentration with a pH/KH reading. You will not be able to find your Potassium level, but dosing KNO3 (Spectracide Stump Remover - found at Walmart) will add Potassium and Nitrate.

If you test your tank water and find no Nitrate present, then add about 1/8 to 1/4 tsp of the stump remover and test again in about 15 minutes (so it mixes thoroughly). You should get it somewhere around 10 to 15ppm (although up to 20ppm isn't a problem). Buy a cheap, but more importantly, easy to use Nitrate test kit, because you will be testing frequently until you set up a fert schedule, and even then pretty regularly. Buy Fleet Enema (or a generic brand, like I use) and add maybe 2 drops after your water change. Keep this level around 1-2ppm Phosphate, but no higher. Sometimes it's hard to find a Phosphate test kit, so I order my kits online. I use Seachem Phosphate test kits, personally. With that high of light output you may run into other algae issues without a more consistent CO2 output. I'd suggest using Flourish Excel along with your DIY CO2 just to make sure there's enough available. For your small tank, it's pretty economical.

you do need to dose micros and macros; plants can't survive on light and co2, those two variables allow for photosynthesis but not growth or life. there's no test kits for the nutrients you need to put into the tank (other than phosphates) that are worth trying; especially the iron kits. testing for Fe is going give you a headache.

you can get away with using the flourish trace mix, or get the ppdm from gregwatson.com; kno3 and k2so4 plus the ppdm will give you a good dry combo for standard dosing or you can get all the individual nutrients required for ei (estimated index).

In addition to dosing ferts, also keep in mind that BGA does not do well in water current so be sure you have plenty of water movement in your tank. I suggest aiming a power head towards the area where the outbreak usually begins.

I suppose it's unpopular and I mean no offense, but I want to disagree with the last post that water current will discourage BGA. I have found that in a magority of the times I've dealt with Cyanobacteria (BGA), that they have been located prominently in the direct flow of my filter outlets, if not on the filter outlets themselves! I find that this type of algae (if you can call Cyanobacteria an algae) tends to thrive most in the tops of an aquarium and near the outlets of the filters.

My advice is to be relentless in clearing this as much as possible by hand, and then keeping water quality as pristene as posible until it is no longer a problem. CO2, as always, is a key factor in controlling any type of algae in a planted tank, so keep it maxed out!