As long as you're bumping up your budget, I'd suggest looking for a refractometer. It's pricey I know, especially when you're trying to do this on the cheap, but it can save you a LOT of trouble as compared to a hydrometer, since many are so inaccurate. Case in point: I was working last weekend and someone came in wanting a water test. Their hydrometer was reading 1.025 but when SG was checked with a refracto we found that it was actually 1.030!My refracto was one of the best purchases I have made for my nano reef- IMO it is essential for a nano because SG can change so rapidly due to evap, especially one that is open-top (not sure if yours is or not).
Good luck!
Your fighting a losing battle there