Want to tie 2 tanks together

[ThatGuy]

I want to tie my 40 & 42 together(one system) without changing all the water in the FO what do I need to do so it doesn't shock my DT. Should I be good if all the parameters are the same?

 

[Tazmaniancowboy]

if the water params are the same I don't think there would be a problem. I was afraid to bring a huge sump and refugium online once, but it was explained to me that it was just like doing a big water change. I had no problems

 

[Nickjr000]

Souldnt b an issue if they r close. If u wanna make yourself more comfortable, swap a few buckets of water between the 2 tanks once a week for a few weeks then tie them together