Water changes

[Lauramichelle]

Ok, my 20 gal salt tank is cycling nicely. No livestock yet. So I'm using this time to research and learn. I already did a 50% water change, but without any lives to worry about. I get my salt water from the same lfs each time.
Now, lets say I have an established reef and fish tank going. It's time for a weekly 5 gal water change. Do I need to match temp, salinity, ph, etc? Therefore, must I get my water days in advance, mix, heat, test and prep prior to a change? Or can I simply heat it and add it. Also, is it considered "top off" water? Or must it be salt water? How long can my tank sustain without a water change if I need to adjust the new water?
One reason for asking is that I discovered that the original lfs where I purchased my initial 20 gal runs salt levels too low for fish. They say otherwise, but I had my water tested at 2 other lfs' and they confirmed it. Now I'm spooked that I may do everything right yet have a disaster due to a poor supplier.
Thank you so much for your help.

 

[Sniperhank]

Yes, you need to match. If you don't, you will stress out all the critters in your tank which can lead to things like ich and death. I only match temp, salinity, and pH personally.

Top off water should be distilled water. The salt is already in the tank, adding more salt water is redundant.

I started off with being supplied saltwater...let me tell you how retarded of a choice that was on my part. I just got my RO/DI on Monday. I have already saved over 20 dollars in water, not even thinking about gas. This is the best investment you can ever make. Spend 100 to save thousand(s). All I do is throw a 5 gallon bucket in my sink, hook up my RO/DI, and turn it on. Then I play with my dog for awhile or clean a room in my house. By the time I'm done my water is made. Measure out the right amount of salt (I use reef crystals), test and heat. Even after I mix it quickly with a wooden spoon I throw a small power head in to keep the water moving around. Even if I'm strapped for time I can make up a batch of water and get back to it the next day, throw the salt in and turn on the PH and heater and go to work... I'm sure you get the idea. It takes 10 minutes of actual effort to do yourself.

 

[Lauramichelle]

WOW! That really sounds great. Would you mind telling me where I can get the RO unit? And how do I match PH? I really appreciate it. Thank you.

 

[Sniperhank]

Ebay for 100 or less. I refused to wait so I spent...150 from one at a Petsmart when I was on my way home from seeing the g/f. Wait a week to get it and have to do a PWC without it or spend an extra bit of cash... I spent the extra bit. While I was there I picked up the biggest bag of reef crystals they had.

For my pH, i keep up with my water changes and keep my tank with good flow for air/gas exchange and I have 8.1 off of well water I distill.

 

[Lauramichelle]

Thank you do much. I'm definitely checking into it. I really appreciate it.