My DIY Auto Water Change system (low budget, high performance)

[Bramzor]

For a cheaper version of AWC, I used a high flow Dosing pump on 24V https://www.aliexpress.com/item/32948192564.html
Placed the second dosing pump together on the first motor, used a motor driving shaft that I created myself (but you could probably just buy it online too).
This should allow an even water change. I used regular RO tubing 3 x 15meter (=50 feet each). 2 of them for the water changes which is about 15 meter away from my tank and 1 for adding RO water from the same technical room.

So the AWC dosing pump which is 1 motor (keep the other one as spare), 1 speed as it uses the same motor shaft and 2 heads. Cost me about 50$? Tubing etc another 10$. You can trigger these dosing pumps using a FMM which can trigger a 24V and you can use the FMM ports for water leakage and water levels. I added my own DIY 2x Inductive Water sensor https://www.aliexpress.com/item/33041900609.html on that FMM to check RO water tank and Salt water tank from outside of the tank. (So no need to run wires inside which can corrode)
You could also use the 2 other ports on the FMM for measuring flow. I have one for measuring flow between mij RODI set and my RO tank. If flow drops, I know the tank is full.

To make sure that I would know if there is an issue with the AWC. I'm also using 3 Optical water sensors (https://www.aliexpress.com/item/32955443010.html) . 1 is shared with your Auto topoff of RO to detect normal water level. The 2 others should be placed above and below that normal water level (Auto fill sensor) about half of the water volume you want to replace (or even lower). The 2nd sensor you put the same amount underneath the Auto fill sensor.

During the AWC (which will only start if water levels are normal), TopOff is disabled. During the AWC an alarm will be given when water drops below the low level or goes above the high level.
This allows you to be alerted when for some reason, water is not equally replaced and off by about 50% of the water you would change during the AWC.

Still have to test out a few things and only started using it since a few days, but already wanted to share how I did it.

 

[Bramzor]

Did a few tests and noticed that there is a difference of 15% between In and Out volume. Luckily its an increase and does not lower salinity over time...

In: 580ml
Out: 505ml
Off by 15%

Which means that every day, I increase the volume with 15% based on a 1% WC each day, so after a month, this would give me a total increase of 4.5l which is a 3% increase in total volume over 30 days. Skimmer cup holds about 375ml so I could remove about 10 cups each month (one every 3 days) and remove 3.75l doing this. This would give me a netto SW increase of 750ml over a month.
Probably a 0.5% water change each day would be better to decrease the total amount of water changed and the total amount of SW water overdose per month.

 

[Phildago]

This adds and removes water at the same time?

 

[Bramzor]

This adds and removes water at the same time?

yes, Auto Water Changes means doing a water change by using 2 dosing pump heads on one motor. Which should replace an equal amount of water. (Although it seems over a longer distance, its not exactly the same). In my case probably because one motor is pushing the new water over a longer distance, while the other pulls the water over a longer distance.

 

[Dr. Dendrostein]

I luv it, I luv it. ..... only thing I would add a bracket on the all thread side opposite the motor, but great simple setup. I too setup auto water changer with two programmable dosing pumps. Did it this way, cause had pumps sitting around, were used for feeding corals, then no longer used.

 

[ozborn99]

Did a few tests and noticed that there is a difference of 15% between In and Out volume. Luckily its an increase and does not lower salinity over time...

In: 580ml
Out: 505ml
Off by 15%

Which means that every day, I increase the volume with 15% based on a 1% WC each day, so after a month, this would give me a total increase of 4.5l which is a 3% increase in total volume over 30 days. Skimmer cup holds about 375ml so I could remove about 10 cups each month (one every 3 days) and remove 3.75l doing this. This would give me a netto SW increase of 750ml over a month.
Probably a 0.5% water change each day would be better to decrease the total amount of water changed and the total amount of SW water overdose per month.

What happens when the motor pumping water out, starts slowing down more than the other, from buildup? No bueno buddy.

 

[Dr. Dendrostein]

What happens when the motor pumping water out, starts slowing down more than the other, from buildup? No bueno buddy.

I know mine I have pre-filters, same setup been running on different tanks, from 1983-1989 and 2017 to present. No issues

 

[ozborn99]

I know mine I have pre-filters, same setup been running on different tanks, from 1983-1989 and 2017 to present. No issues

That's awesome news. I've always been wary of using two pumps that need to stay at the same speed, but it doesn't mean it doesn't work, right?

 

[lilgrounchuck]

What happens when the motor pumping water out, starts slowing down more than the other, from buildup? No bueno buddy.

He’s got both pumps controlled by one motor. If the motor fails, no water moves at all. If the out pump seized up or the rollers loosen up on the tubing there’ll be issues though.

 

[Dr. Dendrostein]

That's awesome news. I've always been wary of using two pumps that need to stay at the same speed, but it doesn't mean it doesn't work, right?

You wanted to work and last, unless one tries and implements an idea, won't know results. I think I would restrict the pump removing or adding more water. My thought

 

[Dr. Dendrostein]

He’s got both pumps controlled by one motor. If the motor fails, no water moves at all. If the out pump seized up or the rollers loosen up on the tubing there’ll be issues though.

Mine being two, if one fails, I either have more water or less, I do 4 gallon per day, 365 days a year is the goal. I do stock up on 3 or 4 of each part.

 

[Phildago]

It doesn't mean two dosing pumps on one motor. I suppose it could be used, but it would be less efficient. You want to remove a set volume of water then replace that same amount. Doing it at the same time is less efficient.

And using one motor makes it so that you cannot adjust both to be equal, if one pumps more or less then you're stuck with it. If you used a water level switch (float or optical, a float valve would even work) to switch the return water pump off (on a separate motor) at a setpoint after all the dirty water was removed then you'd never over fill and always replace exactly what was removed

 

[Bramzor]

It doesn't mean two dosing pumps on one motor. I suppose it could be used, but it would be less efficient. You want to remove a set volume of water then replace that same amount. Doing it at the same time is less efficient.

And using one motor makes it so that you cannot adjust both to be equal, if one pumps more or less then you're stuck with it. If you used a water level switch (float or optical, a float valve would even work) to switch the return water pump off (on a separate motor) at a setpoint after all the dirty water was removed then you'd never over fill and always replace exactly what was removed

As long as you pull it out on one side and put it back in on the other side, it can be as efficient as doing it with 2 dosing pumps. I pull it out where my filtersock is and put it in where the return pump is so efficiency is 100% in my case. I have a nano tank so if you use a slow dosing pump to do the water replacement which needs to run a long time, yes, your efficiency will go down (although not that much and probably neglectable anyway)

Also having one motor will normally add the same amount as the amount that is being removed. Motors can fail, sooner than dosing heads would. Only situations where a difference can be introduced is where there is a long distance between the tank and the pump or a difference in length between in and out (in my case causing a 15% difference), but otherwise, value that is being replaced is almost identical by design (tested on short distance and was off by less than 1%). This will not be the case with 2 different pumps. Never by design. Yes you can tweak it so it will be calibrated and this allows some adjustment but you will have to check this over time as it is not designed to remove the same amount as being put in by design.

Having a sensor to do that is not the correct way either. There are tons of situations where there is fluctuation in water level if you have a sump for example (the reason why ATO goes wrong on a lot of tanks), or if something gets turned off during the change.
I have 3 optical sensors but ONLY as a failsafe to notify me if something is going wrong. For example if for some reason, one pump is not drawing water anymore, water level will change because of the difference of water that is being put in compared to pulled out, and trigger an alert.

It's not easy to create an AWC that has a low possibility of introducing any issues but in my opinion, having a motor with 2 dosing heads on it and having a failsafe in the form of multiple optical sensors is the way to go. Yes, there is a difference in water that goes in and goes out in my case but its a good thing as it will compensate water that is pulled out because of the skimmer or other reasons. And as long as you know this can happen, its an easy check that you can do once a month and correct it if needed. I could have used 2 dosing pumps but I specifically modified it so it would be 2 heads on one motor, for the reasons mentioned above.

Things that require human interaction to keep working properly (for example calibration) will go wrong sooner or later.