I very much believe in Bio Spira, and I believe what they mean is that you put the necessary amount of bio spira in your tank, then add a full load (meaning just that, the total amount of fish that you would have in your tank when your done adding fish, I also think this means that you need to account for fish growth, so obviously you wouldnt want to put in 5 , one inch oscars in a 10 gallon tank.)
The stuff does work, but the owner of one LFS said the jury is still out on the saltwater Bio Spira, and that he believes that you should setup the tank, with livesand, liverock, water then add the Biospira and one or two fish, then in 3 weeks time, you can add the full load of fish 1 or 2 fish per week until your tank is fully stocked with all the inhabitants it is going to have. But this seems to go against my idea that if you wait too long, then the good bacteria wont have enough load to eat, and thus die off to where only an amount of bacteria equal to the bio load put on the tank will be able to survive, and thus if you wait 3 weeks, bacteria may have died off and then you'll be adding too many fish at one time because the bacteria wont be built backup quickly enough like it is when you initially dump the package of bio spira into the tank. Lots of bacteria, needs lots of fish waste to keep alive.
I only have experience using the freshwater biospira, and it worked fine for my goldfish tank, never had an amonia or nitrite spike, and only nitrates are a little high, but thats because thery are dirty goldfish. The otherday I dumped in the bio spira to my 100 gallon tank with an oscar about 40 or so minutes later, and he didnt do well, I thought maybe this bio spira stuff isnt all that, but turned out the Oscar had some disease and it wasnt the Bio Spira.
In anyevent, if you dont add enough fish to a bio spira cycled tank, the bacteria will die off because they will have nothing to live on, which would defeat the purpose of using the product.
Im not bagging on anyone here, but the aquarium hobby seems to be one of those hobbies that take forever before something that's actually good catches on as being good. Bio Spira is GOOD, atleast for freshwater tanks. Hopefully one day I'll have the opportunity to startup a salt tank with it and see what happens, hopefully it's just as good.
// crawls down off my bio spira soapbox and back into the hole of despair, known as WORK.
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As to the original question, Im just not sure, Im no good at diagnosing diseases without actually seeing something. I have fish that will swim in the current all day long, but none of them actually try to scrape themselves like they have an itch. I would not lower your salinity if I were you at this point, if anything I would raise it maybe up to 1.023 or 1.024, my LFS keeps theres between 1.018 and 1.021 because they say thats what the wholesalers keep their fish in, so its easiest for them to keep it at that SG.
What was your acclimation process like? How long as he now been in your tank?