Ok Jeff, there does seem to be some confusion here, so I'm going to see if we can help you get down to business.
An ATO is an automatic topoff unit. It's job is to monitor the level of the water in your tank. When level gets below a certain point it moves clean (0 TDS) water from some type of storage container to the tank until it returns to normal level. Something like this is what folks are talking about
http://www.bulkreefsupply.com/tunze-osmolator-nano-3152-auto-top-off.html
An RO/DI unit is something completely different. An RO/DI unit filters your tap water producing both clean RO/DI water as it has filters/membranes for both processes, and it produces waste water which gets discarded. So if you look at the basic picture here, you plug your common garden hose into the red line, the blue line runs to your RO/DI container and the black would run to a nearby sink or out a nearby window. Something like this
http://www.bulkreefsupply.com/brs-4-stage-value-ro-di-system-75gpd-2.html
As was mentioned already you're really going to want to feed some kind of "greens" aka algae to a few of your fish on a daily basis. If you have a local oriental market you can get some there. It's basically the seaweed wrap stuff that goes inside sushi. If you don't have it local or can't find it, you will probably overpay of you get it from a fish store sold as algae. FOllow this link for some examples
http://www.amazon.com/s/ref=nb_sb_noss_2?url=search-alias=aps&field-keywords=nori+sheets
You'll also need a way to feed said Nori. You have a couple of options here. A rubber band to a small rock works for some people. I personally prefer these. they come with a magnet and just hand inside your tank. There is a version with a suction cup as well that is much cheaper, but to be honest they are kind of a pain as they seem to constantly dislodge themselves.
http://www.bulkreefsupply.com/veggiemag-magnetic-floating-seaveggies-clip.html
For water changes many of us use the good old Brute trash cans as they are food safe. The Grey, yellow and White are USDA Meat safe as well.
http://www.amazon.com/Rubbermaid-Co...sim_328_1?ie=UTF8&refRID=0NAQSN8CARY7MJ1F75K9 Lid Sold Separate
http://www.amazon.com/Rubbermaid-Co...sim_328_5?ie=UTF8&refRID=0E97GQBX37G0K94MWSZN
So the whole water process goes something like this.
1. Figure out what level you like to keep the tank at and install an ATO to keep it there. As water evaporates, you will automatically refill to that level with the ATO to maintain salinity. One of those 5 gallon jugs you have may be useful here as an ATO container.
2. Whenever you go through 1 ATO container or 7-10 days, do a water change. You might have to use two ATO jugs in a 7-10 day time period, but I wouldn't think you would get too much evaporation.
3. For water change, the day before you plan to do the water change, mix up some fresh salt water. I would start by taking your 5 gallon jugs with regular tap water, 2 of them to be exact. then dump those inside the trash can. Take a Sharpie and mark on the outside of the can the water level. Do this 3 times, marking level every time. Now take that water out of one trash can and mark the same levels on your second. Now you're set. Discard the tap water and begin filling one can with RO/DI to the top fill line.
4. Now you'll need some salt and a way to mix said salt. The tradoff in price here is the buckets is convenient, which the box has more in it. If you already have a 5 gallon bucket with sealing lid, just get the boxes. Also keep an eye out as you can frequently find them on sale on different websites including
Amazon http://www.bulkreefsupply.com/instant-ocean-reef-crystals-salt-mix.html . Now you also need something to mix said salt. I personally use larger one but something like this will suffice.
http://www.bulkreefsupply.com/eheim-compact-pump-1000.html . Any decent pump will do, but I will explain why I use a larger pump later.
5. So you mix your salt and bring it up to a salinity reading of 1.022 (fish only you can mix less) - 1.026 (if you have corals and such). You measure this with a refractometer. These work great
http://www.bulkreefsupply.com/refractometer-for-reading-salinity-with-calibration-fluid.html and make sure you calibrate it about once a month with
http://www.bulkreefsupply.com/aqua-craft-refractometer-calibration-fluid.html . As long as your water change bucket of clean salt water lives inside the house within 10 degrees of your tank water you don't need to worry about having a heater inside.
6. So it's now water change day and you've been mixing your saltwater for around 24 hours. Take any only gravel vac and gently vacuum the sand careful not to remove the sand. Fill your second trash can to the first 10g mark. Make sure you have turned off your ATO before starting or it will try to replace the water as fast as you're taking it out. Saltwater out + freshwater in means salinity is going down, which is bad,
7. Now the easy part and the reason we got that larger pump with the 5/8" outlet connection.
http://www.amazon.com/Watts-SVKI20-...TF8&qid=1438339977&sr=8-3&keywords=5/8+tubing . Have one person hold one end of the tubing into the tank, while the second person connects the other end to the pump. Drop the pump back into the water, plug in and drain to your first marked line on your can.
8. Once done filling, swap the pump to the other trash can and drain outside/sink/shower...etc.
And you're done. So if you go every 10 days or there about this would have you changing 30 gallons a month. You can fill the can for SW once a month and only need to fill your top offs in between. The idea here is two fold. It's always a good idea to have some ready made water on hand in case of emergency. This also allows you to simplify your water changes, taking a lot of the headache and time out which usually means you're more likely to do them.
I'll stop talking now, because I may have just lost you and I don't think you asked for a novel but I just woke up and was waiting on coffee to finish. Keep in mind you don't need these exact components as everybody does this differently, but a system like this would give you a good start.
