Merging two tanks into a 75 gallon - recs?


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We are merging a 40 gallon and biocube that have up for almost 2 years into a 75 gallon. Assuming we keep all the sand, water and live rock, we don’t need to worry about cycling again, right?

We have 2 clowns, CUC right now and some zoas, GSP and a hammer. One tank does have a major green hair algae issue so the plan is to switch out that live rock with other cured rock that we have.

does anyone have any recs of things I am not thinking of to manage this switch without killing anything?
Water and live rock really mean nothing. What filter media do you have in the tanks and what are your plans for that?

Let me know the answers to this and I can provide some toughts.
It’s a drilled tank with a sump so the plan was to transfer everything in old sump into new sump including all filter media, protein skimmer etc.
Be careful, tank size becomes exponential. I went from a 40 to 90 (frogspawn and soft coral). And, now more than 15 years later, 450 (SPS & mixed).
Keep about 20% (number pulled from butt) of the water from each tank to dump into the new one, the rest should be new water.

Use the old tank water to rinse/shake all the crap off the rocks before moving stuff over, and redoing your scape.

As for the sand, either rinse it out until its all clear or get new sand. Mixing up the crap in the sand is what will start a new cycle or crash the system.

Make sure to keep the live stock warm during the transfer and youre good to go.