No, you need to either use a power supply connected on the relay box and use RA to turn on/off that port based on your current float switches or use a dedicated float that is not connected to RA to send the signal downstairs.
Optocouplers need power on both sides.
The upstairs one is getting the power from an external power supply (this way you don't have any chance of picking up noise by using RA power supply) and the downstairs can use the one from RA, since it is a short run.
What you are trying to do is avoiding sending wires that are connected to either +5 or GND in your RA through a long wire. It acts as an antenna and noise just travels through to RA, which can cause unexpected behaviors.

Ok. Now I got it. Ok 2 relays it will be..I can always replace all the wall warts with the 12V power module. And that would give me an extra 5 12V ports for something Except it might be good to have all the 12V ports with the solenoid valves downstairs. I hope taxes work out well this year...

I decided what I will do. I am gong to use my computer as a proxy between the two ra's. I already query my ra once a minute. I will look for a flag to allow/disallow water change mode and a flag to enable/disable the ro filling. I will just use a timer with enough buffer to not run into issues (like 60% then fill to 80%. Why waste relays. Plus I can just have it run just a couple of times a day.... Gotta think of all the scenarios.

So I've been thinking of how I'm going to run my salt mixing station. I will use the salinity module and the water level sensor and another pump. The pump will be set as an ATO but for salinity with the water level sensor acting as the failsafe along with a timeout. I can set it to use "water change mode" as the trigger, which would also disable the automatic water change until the new water is ready. Basically, the idea is that when water gets low, I'll run downstairs, turn on water change mode and dump a few cups of salt in. The RA will then start circulating the water and adding RO until the salinity reaches the target. Once there, it will continue mixing for x amount of time before disabling the water change mode and re-enable the auto-water change with the tank upstairs.

The overall idea is just add salt once or twice a week. What do you guys think?

It sounds good.

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Just ordered a 24V solenoid valve with 1/4" quick connects. I will tee off my RO/DI output and this will open up the connection upstairs to fill the ATO reservoir. I'll use the RO/DI pressure instead of using a seperate pump.

I decided I will be setting up my 10G QT tank with the third head on the ametek pump. Even if I'm not actively QT'ing anything, I can use it for rinse water i figure long term it would be better for all the heads to have the same amount of wear.

I received my new ReefAngel controller for the setup. I will be setting up a 5V power supply connected to an outlet on the RA upstairs to a relay downstairs which will be connected to one of the float switch ports. If this input is not "active" i will not run the RO or the AWC.

The float switch in the salt water bin is also going to be connected to the RA so when that flips the AWC will be disabled and I'll send myself an alert.

For the RO I will monitor the reservoir % from my Mac. When it gets to lets say 20% I'll have a cron job to let the other RA know to open the solenoid for an hour or so. If the % goes higher than lets say 90% I'll have the upstairs controller deactivate the control signal and send me an alarm.

The relays that will control the Ametek pump and the RO solenoid will both be powered by the same 24V power supply which will also power the pump and solenoid and each will be triggered separately by a 5V analog signal from the RA. This will give me endless scheduling flexibility and the capability to change on demand.

Now that the RA is here, I can get working on the programming. I'm still waiting on a PWM motor drive and now the solenoid. I'm waiting on zachts from RC to figure out the connectors to go from the ametek to the cheap 1/4" tubing, but I think otherwise I have everything ready to go. Just need a trip to radioshack for some wire and connectors to make it all happen.

These are the relays I picked up, except mine are 24V

http://m.ebay.com/itm/400525119455

Solenoid:

http://m.ebay.com/itm/290836300351

PWM motor controller

http://m.ebay.com/itm/261099568424

Hope the links work...

What's the motor controller for?
I saw the link, but didn't quite get it.
What is that pot and what is POW?

It's too slow down the water change pump to a crawl. Also the slower it run the quieter it is.

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Yeah essentially it uses pwm to slow down the motor but it'll take the 24v signal and send it out as pwm at whatever frequency to get the speed you want.

These pumps are pretty loud. At the end of the day its for noise control.