Connecting a 40 gallon long to a 40 gallon cube?

[rapid]

I have a question and if anyone has done this please chime in with the do's and donts!

I have a 40 gallon cube mixed reef only have one RTBA and a torch coral. 2 Mated clowns, diamond goby, green maderian dragonet, one bubble molly.

I would like to take a old freshwater tank i have had in the past and attach a overflow to it and plum it into my current 20 gallon cube sump that is running my 40 gallon cube. this 40 gallon long tank will basically be turned into a display refugium right next to the cube reef display.

It will have a live sand bed and live rock collected from https://tbsaltwater.com/ Should i not add this rock ? should i add this rock ? ive heard good things about it.

I am also going to grow a bunch of different macros in this tank

what are the pros and cons of this ?

 

[Bosreef]

Don't really understand what your asking?
There no cons really besides more maitence higher volume water changes more salt, more equipment... idk

 

[rapid]

Don't really understand what your asking?
There no cons really besides more maitence higher volume water changes more salt, more equipment... idk

will i have to worry about a tank crash due to adding this ? any parameter swings ? ammonia for live rock will it be a problem ? do i add the rock slowly to it ?