i think i ended up using about 20kg, i had about 40 odd kg and used what looks like less than half but i got to get my scape right rather than just using everything i had and hoping it would come out alright
the FW test is just to check for leaks so you can use tap water, the RO is to get rid of any nasty s, there is no reason you cant do RO as the FW test, it just takes a while to make that much RO
If you get a good salt mix there is very little difference, cheap ones leave you with ionic imbalances as the chorinity is rarely correct, if you have access to fresh sea water it is better but if you get a quality mix I personally cannot tell the difference.
very happy with the substrate, the finer particle size gives a much smoother and brighter appearance .
the vortech has a much better battery back up system, you can use a UPS inline with the tunze and I believe on a 700ah one a single pump will rung for a could of hours, but compared to the vortechs system going 20 odd hours it leaves a bit to be desired