Ok so I want to upgrade from 25 gallon to 40. What is the best way to do it, I want to use the same equipment and put the new tank in same spot...
I want use water from old tank just add 15g of new water, same with the live rock, I don't know about sand bed should I move old sand bed too or replace with new one...??
If you do move the sandbed, my recommendation is either of the following:
1) stir 10% of your sandbed every other day for 20 days prior. Runing Ammonia pads in your system and the new one during the process and for a week after the move. This will limit the amount of ammonia that is released and will help capture excess ammonia that your bacteria cannot handle.
2) When you swap your system over, have a large brute of RODI water standing by to rinse your sand before it goes into the new tank. This will likely suck this time of year with it being cold outside but would be necessary. Also run ammonia pads in your new tank for at least a week. You can always use a fresh 200micron filter bag or I have heard of people using womens leggings to assist in rinsing the sand.
If this is a DSB, I would recommend #2 but be very careful if it is old. the amount of decaying matter can be quite large in an old tank. That is why I keep nassarius snails and a conch to stir my sand bed often!
Good luck!