add RO water and than just buy bags of salt mix. that what i did for my 110 gallon custom. it worked out well after a couple week i got the water perfect than . GOOD LUCK!
i small cube i have my 29 gallon cube and i use a TUNZE 9002 for it but if i had your tank and you need a smaller footprint thats still run power ill do a TUNZE 9006