Upgrading To A Bigger Fish Tank

[Skeez]

Will I need to wait a two months again for the tank to cycle?

[Skeez]

Help, anyone?

[leebca]

Without more information, it is hard to say. But during any expansion, it will take time for the new tank to mature. You don't want to put sensitive marine life in a new tank, even if it didn't cycle or if it just cycled.

[Skeez]

Without more information, it is hard to say. But during any expansion, it will take time for the new tank to mature. You don't want to put sensitive marine life in a new tank, even if it didn't cycle or if it just cycled.

I have a 30g and I'm switching to a 75g.

[leebca]

You are more than doubling in size. If you use or will be adding live rock, the new live rock may need to go through some minor curing. The die off from the new live rock will likely cause a cycle to begin. However, that cycle may be 'weak' and short.

You will undoubtedly be adding more substrate. The substrate needs time to 'seed' (don't bother buying living substrate -- waste of money -- bacteria and benthic creatures are free with live rock and from the air) and the aquarium will need time to mature for marine life forms to be re-introduced.

You would benefit from doing more reading on this:
The Mature Aquarium

Doing this large of an increase, it is almost like starting over, except there can be some shortcuts:
Setting Up a FOWLR Aquarium
If you use the above guidelines, you can skip initial waiting times and extra time with inverts, but still you need to increase the numbers of the clean up crew and with the larger tank you have additional options for that crew.

BTW, using the 'old' water isn't helpful. You can use the old water or make it up new, just so you adjust the water like you were going to make a large water change: How to Make a Successful Water Change

I would recommend you do the reading and take your time.

[reeferguru]

I would use as much of the sand, rock and water from your 30 gallon to add to the new larger 75 gallon tank. This will aid in the cycling time, possibly not causing a cycle at all due to the beneficial bacteria already established.
Good luck!