i wouldnt recommend it at all. my last hydrometer was 0.003 out. salinity is very important to keep right. take for example scatman's tank (no offense to him here, he didnt have a refractometer at the time) He was having problems with corals dying - I checked his salinity with my refractometer it was 1.031, corals getting burnt! this is probably more important on a smaller tank than larger, if you dont get your topup right then salinity can swing more (yeah yeah, more evaporation on larger tanks but still the proportion is greater on smaller tanks!) this is not something you want to cut corners on, especially if you are investing money on nice corals, then be smart and invest the money on the right equipment to test water parameters. that includes quality test kits like salifert too!!!
you can have my old inaccurate one!!! :lol: