Automated water change system cheap

Hi there i am trying to design an automated water change system for my discus tank budgeted.
Below the details i am trying out please comment .
The overall simplicity :
Attachment 125398

Basic concept : (full automation)
1. Pump is activated at a certain time to pump fresh water into aquarium. (manually should also be available)
2. If aquarium is full the overflow piping will be activated and water will flow to the drain.
3. Water level sensor for reservoir tank will be activated and pump will stop pumping water. (adjust sensor height to allow how much water to be replace.)
4. After reservoir pump is shut off auto trigger valve for tab water to flow in.
5. Tab water will fill in until sensor is activated to stop water from flowing in ; Overflow piping is also needed to just in case there is electronic failure.

Details on the reservoir tank :
Attachment 125399

Cost will be updated when i search through ebay lol.

Because your fresh water will be mixing with old water you will need to monitor your nitrate levels. If your nitrates are 10 and you remove 75% before you fill your nitrates will be 2.5. in your scenario your filling is what triggers the draining so your nitrate/waste removal will be variable. You could mitigate that by having a small additional pump in your aquarium that drains the tank before the clean water refills it.

You will have water in the pipe/hose from the pump in the lower tank to the upper tank. Once the pump in the lower tank quits pumping how does the pipe lose the siphon?
Pat

Hmm... I am guessing a simple check valve would do the trick, thanks for pointing that out.
As for the nitrate It would be be diluted ... I will still need to do the **** cleaning for the discus daily...keeping things simple.

"As for the nitrate It would be be diluted"
True, but you have no idea how much. As the tank fills you may only get a 50% dilution on a 100% water change. To me that makes the system inefficient and not cost effective. If you're going to go to all the expense & effort of solenoid switches etc, it doesn't make sense not to mitigate this issue with your plan.
It is your set up though, so you do as you please, I was merely pointing out an apparent design flaw as the intended purpose of the system seems to be to provide high level water quality and ease with your maintenance. :)

Any setup like this using dilution is going to be inefficient. What it does accomplish is the standing around time. During water changes is eliminated. It’s a trade off.
As far as breaking the siphon on the output to the drain, all you would need to do is add a vent to the line so a siphon never starts. Also it would need to be a bulkhead through the side of the tank.
And the other thing to think about is automation that requires electronics to function will eventually fail, so ensuring that when it does, it doesn’t kill fish or flood the house is the priority over making time to do water changes. In my case I went for a faster process and less electricity being used.My .02