Upgrading aquarium size question

[Backreefing]

Hello I’m upgrading my 20 year old 37 gallon reef to a 90 gallon. But I want it as smooth as possible. The 37 is sps and just a couple of zoas .
Some of my ideas are to use the old water changes water for the new aquarium. There is nothing wrong with the old water. But if most of the new aquarium is filled with the 37s water then ?
The 37 has agronite crushed coral. So will the 90 gallon aquarium.
Another idea is to add agronite gravel to the 37 to increase the amount of gravel, to later transfer to the 90 . And to vacuum the old and add some new . Probably 1/3rd will be new at the time of the transition.
I also thought to get a cheep fish , like a blue green cromis. To keep the cycle going. Just to help the 90 before the transition.
My main concerns are about water parameters being identical during the transfer.
I also thought to just put the new aquarium together new water and all , then spend the day before the transfer mixing the two aquariums water together.
What do you think ? Thx

 

[o2manyfish]

The water is not what you want - it's the rock and gravel/sand from the old tank. Matching the water params from old to new is easy. Check your temp, salinity and alk. Everything else important is going to be your filtration.

Dave B

 

[Coralreefer1]

Transferring your rock, sand and say half of your water from the old tank will ensure parameters will be close to the same. This will also save you the headache of mixing and adding all new saltwater to the tank. Also, as for a cycle, you shouldn’t experience one since your transferring everything from the 37 to the 90 gal. Just go slow as you introduce new tank mates so that the bacteria can populate to handle the increased bioload
Good luck...