water and fish would be good!! seriously tho 75g gives you loads of options depends on what fish you like. been having the same dilema myself lately as im upgrading from 26g to 95g. im going with my red tailed black shark pictus catfish a plec my kribs a blue acara was gonna have a sverum but apparantly they are buggers for eating plants maybe some keyhole cichlids rams rainbows the possibilities are varied and vast . my advice would be to decide which type of fish you like best and then use a site like thinkfish.co.uk or similar to see what will go together and take it from there