Since the tank has had freshwater fish in it before, you'll need to clean it out real good.
DO NOT!! use any chemicals to clean it. NO soap, NO BLEACH, NO Fantastic, NO comet or ANY chemicals of any sort. Not even dishwashing liquid -- NOTHING.
Scrub it with a brand new sponge from the grocery store. NOT one of those sponges that has anti-bacterial stuff. A plain old regular old cheap sponge.
Use warm water and baking soda as a mild abrasive if you need to scrub off any hard water or stains. Baking soad is the only thing you should use.
Rinse the snot out of it. Rinse and rinse and rinse and rinse and rinse.
Set it on the stand and fill it up. Leave room for salt, rocks, sand, etc. Don't put the rocks, sand etc, in just yet. Fill it up and stop about 6" or 8" from the top. Weigh or measure your salt mix and dump it in. Just dump it in. No big deal.
Now start a powerhead or a canister or some type of filter and get the water pumping. Let it pump for a couple 2 or 3 days to make sure all the salt crystals are dissolved. Get out the hydrometer and take a salinity reading. You want 1.022--1.025. Add salt or freshwater to adjust.
Put your sand in the bottom and toss in your rocks. Landscape (aquascape) the rocks.
Top off the tank with saltwater after you have all the rocks, sand etc in the tank. Fill it up to within 1" of the top.
Turn on all the filters. Get the skimmer cleaned up the same way you did with the tank. Get the skimmer in the tank. Turn it on.
Your lights aren't worth a hoot. You need more than 40 watts of light for a 75g saltwater tank. It's a 48" long tank, so start looking at compact fluorescent lights or metal halide lights that are 48" long. They make combo lights that have compact fluorescent lights AND metal halide lights. You want about 3 or 4 watts of light per gallon of water, so with a 75g tank, your going to want around 225--300 watts of light. You can do it with less light, but these types of fish really need good lighting to help them stay healthy and grow.
Cycle the tank.
The tank needs to undergo a cycle process before you can put fish in it. There are bacteria that need to grow inside the tank. These bacteria like oxygen--same as almost every other living creature on earth--and they will grow, but they need something to eat.
Go to the local grocery store and buy a fresh shrimp from the deli. Raw shrimp with the shell still on. The kind you would toss on the BBQ at a dinner party. Get 2 or 3 little ones or get one big prawn. Either way.
Toss it in the tank. Let it rot. It will STINK!! It will get SLIMY!! Let it rot. It's going to take at least 3 or 4 weeks for it to rot. Maybe as long as 6 or 8 weeks.
When the shrimp is 100% GONE and completely decomposed--you're ready to test the water. It's okay if the shell is still in there. But all the meat should be gone. Give it a week AFTER the shrimp is rotted. Let it settle. Relax.
Get a test kit and start testing for:
Ammonia
Nitrite
Nitrate
pH
Alkalinity
When you have ZERO ammonia and nitrite, your probably okay. Test the nitrate. If you have more than 5 or 10--then you need to change about 10 gallons of water and get the nitrate back down under 10. Mix up 10 gallons of saltwater a couple days ahead of time. Get the salinity correct. 1.022--1.025 Let it sit around for a couple days or even a week. Put a loose fitting lid on it to minimize evaporation. Stir it up once or twice a day.
Check your salinity. 1.022--1.025 If it's higher than that--add fresh water to lower it. Water evaporates out and makes the salinity go up. Salt does not evaporate. Always use freshwater to top off and get the salinity back to where you need it. NOT saltwater.
Go get a couple SMALL fish when your ammonia, nitrites and nitrates are ZERO. Not 7 fish and an eel and 16 snails and 3 little damsels. Get ONE or maybe TWO little fish.
Acclimate them slowly. Takes about 2hrs--4hrs would be better. Set the bags in the tank and let the temp equalize. Takes 15--20 minutes. Go have a snack or toss a load of laundry in the washer. Relax.
Open the bag and pour 1 shot glass of water FROM YOUR TANK into the bag every 15 minutes. Leave the bag in the tank. If the bag gets full--take it to the sink and dump out 50% of the water. Add a shot glass of water every 15 minutes. Do this for 2--4 hrs.
NEVER dump the water from the bag into your tank. NEVER. Once the fish are acclimated, net them out and put them in the tank. Dump the water down your kitchen sink. You don't want even a single drop of that water from the fish store in your tank. Ya don't know where it's been.
That should get ya started.
Welcome to your newest addiction.
