DIY auto water change system. would it work?

[Alangarcia]

Hello reef community! Im new to the hobby currently working on trying to setup a 20g nano cube saltwater tank. I want this tank to be as little maintenance as I can possibly make it and with that in mind I wanted a automatic water change system to eliminate the need to haul around 5g buckets of water. However with with the Neptune dos being out of the budget for me and with cheaper options seeming to be unreliable from customer reviews I came up with an idea and drew it out shown in the attached file below. So I wanted to know if this idea I had in mind would actually work? Is there a major flaw in this design that I am unaware of? Now let me get into how I plan this system to work. It starts off by getting water from a water line to a RO/DI unit and from the RO/DI unit run a line to a RO water reservoir (5g) for ATO purposes and run another line to a saltwater reservoir for the AWC system. From there add one submersible pump in the saltwater reservoir and another same submersible pump in the back of the AIO fish tank and both submersible pumps plugged into the same programable timer outlet set to turn on and off 1 day out of the week for a certain time depending of how many GPH the submersible pumps will push out. So the idea here is that since they will both be running at the same time and speed, the pump in the fish tank will pump out water to a drain line and the pump in the saltwater reservoir pumping new clean water back into the tank not setting off the ATO sensor because the water line should remain the same and that's it. Thanks guys!!!

 

[jomatty]

Even if you use the exact same pump my guess is that there will be differences in amount of water pumped. It may be minimal enough that periodic adjustments would suffice, but I’m thinking it may cause you problems.

 

[Larry L]

If I were you I'd do an experiment with the two pumps and three buckets before working up anything more permanent (you could plug both pumps into a power strip and turn the strip on and off). I think it would be almost impossible to get the two pumps to pump the exact same amount of water during the same period of time, due to differences in head pressure caused by the plumbing and due to manufacturing differences in the pumps themselves. You're also going to need to be really careful that the pump that is pumping used water out of the tank doesn't start a siphon that keeps going after the pump shuts off.

 

[Ucyibd1]

I used to have a Masterflex peristaltic pump that had stackable heads. I put two heads on it and one head pumped out tank water and the other pumped fresh saltwater from a holding tank back into the tank. Both heads were the exact same and it worked great. It had adjustable speed and I put it on a timer to run 4 times throughout the day.

 

[Reef-junky]

+1 not going to work

The ideal way to do it would be with a pump like this however It’s probably cheaper to buy the automatic water changer.

 

[raketemensch]

Why not use float switches to determine the amount of water, rather than running pumps for a defined amount of time?

 

[Reef-junky]

Why not use float switches to determine the amount of water, rather than running pumps for a defined amount of time?

Because they are known for failing.

 

[Joekovar]

If you use DC pumps, you can use flow sensors and buck converters to tune the pumps after they're in place. You're going to have to check them regularly however because they're going to get dirty, and wear at different rates. The good news is that tuning them by adjusting the voltages on the buck converters is easy once they're setup.

An alternative would be to put your display drain inlet at the precise location in the tank where a siphon will break when X gallons of empty space is at the top of the tank, turn off your ATO, turn on the drain pump just long enough to start a siphon then turn it off, turn on your fill pump long enough to bring the water level back up, turn the fill pump off, then turn your ATO back on.

You'll have to keep an eye on salinity more carefully doing that though, because your ATO could hide your fill pump weakening/failing.

Ultimately, I think a safe route is to setup such a system, but needing to interact with it between each step.

 

[Reef-junky]

Honestly what you are going to spend on two decent pumps and to set this up you might as well just get this. The only pumps that are going to be accurate enough would be dosing pumps.