Pool store is about the only place to have metals tested, unless you want to buy the kit yourself and test, but I think they're too expensive for one-time use....

I know there's a lot of information out there, and it seems very complicated, but it's really not--it just takes practice. Eventually this will all begin to make sense and you'll wonder why you thought it was so hard!

Get some chlorine in the pool--0.4 ppm isn't enough to keep the algae away. I would put a gallon in today, and then if you plan to shock it, wait until tonight when the sun is off the pool and do it then. Can you tell if you're losing chlorine overnight, or is it just during the day when the sun is out?