Hi BudNini, and welcome. Jtratcliff is right about the amount of acids and tannin but I guess I would argue that any recipe that advises you to add a specific quantity of acid to a must BEFORE you have tasted the finished product is not a recipe that you want to follow. Why are you adding acids to the must? The yeast don't need a particularly high acid bath. to do their thing and honey has no chemical buffers so adding acid at the start CAN create real problems for the yeast because those critters call it quits if the pH of your mead drops below to 3.0 or a little below that.
But here's the thing: you asked can you multiply a recipe designed for 1 gallon to make 6... and so when you ask that question you tell me that you are not a seasoned mead maker, and if you are not a seasoned maker of mead why are you leaping into making 6 gallons of what might turn out to be very poorly made mead when it would be a great deal less expensive AND a great deal easier to drink a single gallon of this mead. If you made 6 one gallon batches of mead serially rather than 1 six gallon batch you would (or should) be a far better maker of mead after the 6th batch than you will be after the first.
Brewers love to brew enough beer for their city every time they take out their kettles but there is no legal requirement that you need to make 6 gallons of wine or mead just because someone says that it is just as easy to make 6 gallons as it is to make one. It is true: it is just as easy but it is also just as easy to make six gallons of barely drinkable mead or wine as it is to make one. AND - in my opinion - making a good traditional mead, a naked mead, basically just yeast, water and honey, which is really what you are making (no fruit, no spices, no herbs, no nuts to hide flaws) takes some skill... Your money, of course. Your mead, and you are not asking me but if you were I would suggest that you make a one gallon batch , perhaps even with less honey, because the higher the % of alcohol the longer you may need to age this to allow for more of the faults to quietly fade away. Good luck.