Tank crash

my friend decided to jump from a 40 to a 90. before switcing anything over i warned him if he moves all it may crash. I tested his water with a hydrometer. it tested 1.028 a lil high we all agree so i told him when mixing up the 90 take 15 gallons treat it with aqua clear but no salt to drop salinity.of course he had to add anothe 50 gallons of water we mixed up the other 35 gallons with salt this morning his tank was reading 1.015. I told him thats because the salt still hasn't all disolved. he was using the instant ocean salt mix.ok so heres the ?
1.by adding the 15 gallons non-salt drop it that low
2. how long does it take for that amount of salt to dissolve into a tank.
3. by using the old 40 and throwing in 50 new water will that cause a mini/full cycle?

 

Water can be tricky

Hey, now is something I can give some hard earned advice on. I mix all my own water and maintain a 30 gallon water/rock cycling tank just in case. I've experimented quite a bit and this would be my advice.
1) 15 gallons shouldn't dent the salinity that much on 90. So...
2) A few minutes. I *highly* recommend having some sort of container (from an actual spare aquarium to a trash can) to pre-mix all your water. It might be a pain but once you get used to it it doesn't take much time or energy to set your rig up. I use a 20 gallon HOT filter (because all you really need is some circulation), a cheap heater and a large plastic tub. I'll point out also that most hydrometers are not calibrated for temp (most have a chart included) and will only read correctly at normal aquarium temps. In short, mix the water overnight if you can but the salt should dissolve in a matter of minutes if you stir it. What I'm guessing happened is the SG (unless you're using a professional hydrometer) read inaccurately because of the temp of the 35 gallons and it really needed more salt added. Don't trust the instructions. I often have to add a little more than they recommend to get "perfect" water. I use Oceanic.
3) That will start the cycle but it's always a good idea to get some "acceptable risk" fish/rock/etc to get the biology of your system used to itself. The system will be unstable for a few days at least, depends on several factors.

 

http://www.3reef.com/forums/asap/possible-tank-crash-63306.html

 

i dont know about the crash but my tanks cycled in 3 weeks and i did the same thing a few months ago when i got it i had the old 40g of cycled water and i made 50gals more. i used prime, and coralife salt. if you want the tank to cycle fast have 90pounds of liverock. 10p LF/each 10gal and your tank should cycle in around 3 weeks.