Fox Farm has powdered bloom boosters you should look into if you like FF. I've used Beastie Bloomz at the end of week 4 and 5 in the past and cha ching in the final weeks of flower. Use once per week.
I personally go straight water for all of week 9 of flowering before I cut. The key is to not over do the nutes in the first place. I'm not sure what difference the last week of water makes honestly but I've always done it.
Silica is important and I use Armor Si as well. I always add it first when mixing up a batch of nutes. You'll want to add it to the reservoir first before adding anything else to the water.
I've used strong powder bloom boosters and still had good tasting sweet bud. You can easily burn the roots with them tho but if used correctly I don't see an issue.