Did you cycle? Is it the 10 gallon?
I am assuming its your water parameters, I would recommend going out and getting a liquid test kit, preferably the API master test kit to test your water (most petstores use test strips which are highly inaccurate ). The ammonia and/or nitrite is the one killing your guppies, I would recommend doing Partial water changes every day until your parameters go down to 0 (exept nitrAte, it should be at 5-20)
Another of whats killing your guppies could be your angelfish or algae eater (Depending on what it is, is it a Chinese algae eater?). Angelfish need 30 gallons or more and could get aggressive in cramped spaces.