I remain skeptical that 5 drops in your 75 gal had any effect at all. That bottle is 1500mg/oz of Vitamin C. One drop is 0.002 oz (rounding up). In other words, you are adding 15 mg of Vitamin C to your 75g, which results in a concentration of 0.05 ppm. All evidence I've come across and documented in other threads show massively larger concentrations required for any effect, with 50 ppm being the most commonly cited concentration. That's 1000x higher than what you are dosing.
To add to that, Vitamin C is only viable in the tank for 8-9 hours before it is no longer providing any effect. Dosing once per week does not maintain any consistent concentration available for use by corals. Perhaps there is something else in the bottle which is providing some benefit, like lithium in Tech-M against bryopsis.
