first the refractometer is a real nice tool. personally i don't own one. but what i did was test a dozen of the ones you dip in the water and where the arrow sits, then that's your salinity. wrong i couldn't get 2 of them to be the same salinity level. so i tested a dozen of the glass hydrometers that float in the water and they all read the same, very accurate. i scoop a pitcher of water out of tank and drop in the hydrometer to check my levels because if you just put it in your tank it will just fly around like a bobber from the powerheads. second go to wallmart and get 2 gallons of distilled water < i use di water but it cost me 600.00 for the set up and a 100.00 every 1000 gallons>. take the distilled water and dump it in your 5 gallon bucket, add a little instant ocean at a time stirring till it clears up and stir again. check your salinity until it gets around 1019-1021 and temp at 79. now take your empty gallon jugs and remove two gallons from your tank. now gently without stirring up the sand pour the fresh mix into your tank. do this twice a month. and between water changes if you have to add top off water do not add salt, salt does not evaporate . three do not over feed your tank. i feed my fish sea veggies only, my meat eaters get fed once a week or two. most fish in captivity are vegetarians. i would add a emperor 400 hang on filter to properly filter that tank. but don't just remove your old just yet, add the new filter along with your old one and let them both run for about a month and then you can can remove your old one, the reason is you want to build up some biological bacteria in your new filter first. and don't play with anemones till you have a tank for them it takes a little designing to keep them getting in power heads. every body wants one and ever body learns a smelly lesson. saltwater is easier than fresh so just calm down and don't make it complicated. and dont get suckered into buying some miracle drugs to fix something that's going wrong in your tank, there are none and you will end up discouraged and be another person that USED to have saltwater. i have been doing this since 1979 there are not to many people can say that.good luck and the main thing is patience.