Vacation advice! Leaving my tanks to my clueless room mate...
 

So I leave for Mexico in two weeks. My room mate knows nothing really about aquariums. Do I write a problem /solution guide? With pictures.
The food is okay since I bought kind of a weekly pill box for each tank.
I also clearly labeled water levels.
This is the first time I'll be away for three weeks.
Any advice would be helpful.

here's what you need to do billy(your name is billy right, well it is now)
first thing you need to do is buy a desert eagle( preferably gold in color)
now prepare a nice diner(you have a girlfriend,get her to cook), now invite your room mate to dinner and have a few laughs and share some stories.
now billy this is where it gets interesting, you tell your girlfriend to leave and then you pull out the desert eagle and put it on the table (if you were wearing shades while having dinner, pull em out in style). now tell your room mate that you are going to paris (whats that you are going to mexico, well you changed your plans).
Billy explain to your room mate that maintaining your tank is a serious buisness. now in style slide him a paper that has all the instructions (make sure they have pictures on them). tell him to follow it down to the last letter. put contact details all of them (mother,father,sister,brother,priest,dog,cow). explain to him in a deep tone that you have a certain set of skills that you are prepared to use on him if he doesent keep your tank in order.
once all this is done get up put your shades on and walk away (it would be preferable to light a smoke at this point for further effect)
alternatively you can just higher a guy for a month to do your tank cleaning, plenty of stores offer a cheap one month deal

Assume your roommate needs things spelled out like a four year old would. Anticipate how things might go wrong and write out solutions... for example what if your skimmer overflows, what should he do? What if the return pump jams, what should he be looking at to make sure things are working. So many of the little "checks" we do in our tanks are so second nature we don't even think to look at them so make sure you write them out in good order.

Have backups that he can easily use, like a backup return pump, backup heater, etc. Have instructions on how to swap them out. Tell him which store has good ro water if your RO unit craps out. Call a friend who is local and knows about the tank, see if that friend would mind being an emergency contact number.

Good luck

Set up an ATO if you don't have one. And get an ice cube tray filled with potioned feedings and water so he just has to throw one in and there's no guess work. don't let him dose anything, and if you can have a fellow can reefer stop by and check on things. Should be no issues I go away for a couple weeks a year and leave a roommate in charge.

I'm not sure adding a potentially disastrous piece of equipment like an ATO just before you leave is a good idea. I would want any auto device running for a few months before I trusted it unattended.

Show the roommate how to log onto here!!!!

I agree. But salinity swings can be one of the worst things for all members of the tank and depending on the tank size it doesn't take long for this to happen. Marking water lines is a safe way to go but this is assuming the friend isn't a sleep over at a girlfriend/boyfriends for a few nights and forgets stuff easily. I think an ato with floats etc. Is pretty tricky but a pressure activated solenoid with a sturdy fastening system is pretty safe. It's a gamble on both sides.

I do it all the time. Just have a 25 gal full of ro water beside the tank and instruct the person to just add water up to the line in the sump ( use black marker to draw line on sump glass). Turn skimmer down a notch ( less chance of overflow) and only feed every other day. Don't add any additives during this time. After 3 weeks, you might come home to a tank that's got a lot of film algae on the glass, but everything else should be ok.

make everything simple. Auto feeder ect. unless your leaving soon and can't test anything for a week at least. contact a fellow reefer friend and ask them to check on it. You can return the favor when they go on holidays.