transfering water... too little

[pastina]

so im all set up for my tank switch, i got a 15 gallon tall ready to go for all my 10g's stuff
heres where im mixed up, my 10g only holds 8 gallons of water, i figure ill only be able to use about 5 gallons of it before it starts to get yucky and cruddy at the bottom
now the 15 gallon im figuring will only hold about 11 gallons once filled with rocks, sand etc

so is it ok to use 5 gallons from my old tank with 11 gallons of clean new ro water? or will this mess things up??
am i better off not using my old water and just going ahead with brand new ro water instead??
i dont want my live stock to be killed by sudden pure water (shrooms, zoa's, inverts and 2 clownfish)
i dunno im confused lol

[Wiskey]

I would mix the Ro water with salt first

Use the 5 gallons you can, then the rest you need to use new, I've done it without too much trouble, just make sure the perams are as close as possible.

Whiskey

[pastina]

so only using 5 gallons of my own water wont cause any issues?? im just thinking like ill get a cycle and die off's
i got all the salt mixing now in buckets waiting for the transformation tonight hehe
i gotta post before and after shots

[Wiskey]

It didn't cause problems for me, but your results may vary.

Your not adding any new LR or increasing the bioload, or using the sand from the old tank are you?

Whiskey

[pastina]

no im not using the old sand at all. im using my live rock and today i bought one 4 lb peice of fiji fully cured live rock, i would have bought more but this store was a total rip off, one rock was 29.99
we didnt feel like driving all the way to that petplace for goods so i went local
the rock was kept in a display with fish and inverts so it shouldnt be a problem. its kinda big though, id like to crack it in half