Bidirectional peristaltic pump with checkvalves

chimbo84

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I have just added a peristaltic pump to my DIY tank monitor/director. It is a raspberry pi with Atlas Scientific probes and pumps and has been working flawlessly so far.

Right now, the ATO function is set to add RODI water in 5mL amounts every minute as long as the salinity measures >35.1ppt. I will eventually be putting a water level shutoff on this as well just in case something goes wrong but for now its been reliable and safe (I only have a 1gal RODI reservoir to limit any catastrophic failures of the system until my water level shutoff is in place).

Anyways, I would like to implement an auto water change system using a second pump and two containers (one empty for dirty salt water and another with fresh salt). These pumps are not cheap so I am wondering if it would be a good idea to run one pump with check valves and just run the pump in reverse to remove water from the tank (check valve opens to the empty container and closes to the fresh water container) and run it forward to add fresh water to the tank (check valve closes on dirty water container and opens on the fresh salt water container). This way I could run the pump alternating between forwards (fresh water in) and reverse (dirty water out) in 100mL stages to change out as much water as I want.

Is this a bad idea? I have attached a quick diagram to indicate what I am talking about. There would be some "overlap" of the two solutions (dirty and fresh salt water) but I could tune that out by adjusting the amount that each stage doses.

Capture.JPG
 

NeonRabbit221B

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I can't imagine why this wouldn't work with checks but @Ranjib has setup a few AWC systems on his reef-pi setups.

I wouldn't advise using a probe to control an ATO. Probe readings drift, need to be calibrated and lack the key metric you want to actually control. Water level. Salt doesn't evaporate so using a float and/or optical would be safer and use the probe as a pure readout for redundancy and alerts.

Edit: You will 100% need a float/optical level sensor for AWC as the tubing degrades overtime and the amount of water dispensed will vary overtime.
 

Ranjib

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I would second that advice. Salinity probes are expensive and notoriously finicky , compared to robust float switches. Hence water level based mechanism is safer for over salinity monitoring based solution .
With that said, i would still say go for it if you really want to try this route . Have some safeguard (like total run time per hour or day ) and see what happens. I have a feeling that their will be delay in water addition to detectable salinity changes and that may cause some swings. But without testing its hard to say. I’m personally curious to know how the water addition impact the salinity level (delay, proportion and rate ),
Godspeed
 

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