Starting a 450 g reef to existing 750 g reef


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I thought a 750 gallon tank would be big enough, but the corals are getting out of hand. I recently built a 450 gallon tank to move some of the larger colonies to. My original plan was to have a completely seperate system, but in the end, decided to plumb them together.

So its all set and ready for sand, rock, and water. My worry is that in tying them together, I'll be adding 450 gallons of water to the display, which will change the water parameters which have been perfectly stable for 3 years.

Looking for thoughts on this. Maybe some possible problems I havent thought of.
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It will be like doing a significant water change if you run the return to the 450 at full flow at 4-6x turnover rate at first.

Set-up and fill the 450 as desired and keep the lights off to minimize problematic algae growth. Slowly open the flow of the return from a trickle on the first day and slowly increase the flow over a period of a week to your desired flow rate.

This method shouldn't shock the corals of the 750 significantly but always keep an eye on their response after each increase of the return flow of the 450.