I might buy a 125 Gallon Tank 72 inches long and combine two smaller Tanks into one
 

I am thinking of Combining two 55 Gallon community Tanks into one 125 Gallon Tank.I would buy a used 125 Gallon Tank and put all the Sand from both and all the live Rock 80 to 100 pounds would easily fit into it.Both 55 Gallon Tanks are 48 inches long and 18 inches high and 12 inches wide.The sand bed in each is Deep 3 to 4 Inches Deep.I would like to buy a 72 inch long Tank 18 inches High and 12 inches wide. A total of 20 Fish between both Tanks most are Clowns and some Damsels.There are some soft corals in one Tank I have a Strong Lighting system on the Tank currently.These two Tanks are over two years old.How Stressful do you think it would be on the Fish and how bad do you think it would cycle again.A long 125 Gallon Tank is what I really want and is a Dream Tank for me.Has anyone ever done this and how did it go for you,I would prefer people with this kind of Experience to give some good Advice on this Subject.I might not do it if it seems to Dangerous on my Fish.The two Tanks have one Purple Tang yes a Purple Tang in a 55 Gallon Tank that is how it is.Seven Black and White Clown Fish one pink spot Goby and one splenids Dottyback and one Harriquin Basslett 6 various Damsels two pigmy angel Fish.Well that is between two 55 Gallon Tanks.If you have experience in combining Tanks I would appreciate your Advice Thank you.If you dont have experience or Helpful Advice on this Subject then you probaley cant Help me Thank you Snapper66.:)

A 125g is 72" long 18" wide and 22" high. The dimension you gave above would only be about 70g. I did the same thing about a year ago. Buy new sand and seed it with a couple cups from your 55g tanks. Stirring that up and putting it into your new tank will cause more harm than good.

You shouldnt see much of a cycle. If you want add one of the 55g tanks and wait a week. Then put the second one in. I would look into adding more LR. I have about 300 lbs in my system(not all in my tank ofcourse). When I moved everything over I didnt lose a thing. You can read up on my thread if you want. Start on the second page.

[url]http://archive.reefcentral.com/forums/showthread.php?s=&threadid=1043104&perpage=25&pagenumber=1[/url]

Thank you AquaReeferMan for the Advice and Help

I just transfered a 65g into a 125. I had no problems and haven't lost anything. Don't re-use all of your old substrate as stated above. It will seed quickly. Your fish will probably sterss a little but I doubt it would be enough to hurt them. Good luck.