Automated Water Changes. Part 1: Dual Head Peristaltic Pumps

DBR_Reef

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Automatic water change systems for saltwater tanks


So, I’m planning on doing a few videos on automatic water changes. I’m hoping that this can provide a good reference for people interested in setting up automatic water changes, but confused by all the options and unsure what would work best for their tank. I’ll make an overview video at the end, but the three types of systems I have seen out there rely on dual head peristaltic pumps, float switches in the sump, and external reservoirs. If you know of another type, please let me know. There are a lot of variations on these types, but the concepts are all the same, and even two of the methods I’ve listed are really a variation of each other.

We are going to start out with the dual head peristaltic pump method. What we will be doing here is using 2 peristaltic pump heads- one to pump waste water out of the sump, and the other to pump fresh salt water into the sump.

So what are the benefits of this system:

· very simple
· very reliable
· Compact
· Can be low maintenance
· Stability from more continuous water changes

Downsides of this system:

· There is almost always error in the amount pumped between the two heads
· Pumps are often expensive
· Must replace pump tubing at regular intervals
· Limited in how much water can be changed by size of pump
· Pumps can be noisy
· Slower, more frequent water changes are slightly less efficient at changing water.

While more frequent water changes provide greater stability to your tanks, you effectively change less water. A balance needs to be struck between frequency and amount. Calculator to get effective water change volume: https://www.hamzasreef.com/Contents/Calculators/EffectiveWaterChange.php. But here is the basic idea- if you have a hundred gallon tank, and you replace all the water in the tank in one go, you have done a 100% water change. If you change 100 gallons, but you do it in 2 batches, then both times you change 50% of the water, but you have only changed 75% of the total water volume.

The more important concern, is the error between the 2 heads. So I’m going to use this setup as an example. I ran this pump for 30 min and the difference in pumping was 250 ml less in the tank side than the FSW side. I think tested how much water the pump was pumping, and it pumped 1000ml in 4.5 min. so over the course of 30 min it pumped 6666 ml, or very roughly 2 gallons. Since I had 250ml of error, this equates to 3.7% error between the 2 pump heads. This might sound like a big problem, but it is easily fixed. Lots of reef keepers shoot for 1.026sg or 35ppt. 35 ppt means for every 1000 units of water, we have 35 units of salt, of 3.5%. To solve our 2 pump head error problem, since we are pumping in less than we are pumping out, we can pump in a more concentrated salt solution, and let out ATO make up the rest. So we have a 3.7% error, so if we multiply our desired concentration, 35ppt by 103.7%, or 1.037, then we get our needed FSW concentration, which is 36.295ppt, or 1.0274sg. You can use this calculator to translate between the 2: https://www.hamzasreef.com/Contents/Calculators/SalinityConversion.php

There are a lot of these 2 head pumps out there- the most common type uses Cole-Palmer pump heads connected to a motor block- masterflex is a common and good brand, but any continuous duty rated motor is fine. The pump head are interchangeable and stackable, meaning that you don’t have to buy a 2 head unit, you can buy a single head unit and add a head. The heads also come in different sizes; here is a link to the different size heads and their pumping capacities: https://www.labmakelaar.com/fjc_documents/masterflexpumpheads.pdf These pumps are expensive new, but can often be found under $100 on ebay. If for some reason, you are looking to buy new stenner makes a dual head pump for dosing chemicals to pools. http://stenner.com/products/pumps/double-head-adjustable-output

There are other options out there. You can even get a really small 2 head Chinese pump for $30. I’m not sure how long they would last, but they are cheap. https://www.ebay.com/itm/Dual-Head-BPT-Tube-Lab-Dosing-Micro-Self-priming-Peristaltic-Liquid-Pump-New/192370986242?

A variation of these dual head pumps is the multi-channel peristaltic pump. These have a single head that holds multiple tubes. They often have more rollers, and may be more accurate. However, they are often not quite as bulletproof.

Another option to those pumps is to use 2 separate calibratable dosing pumps, like a liter meter, a dos pumps, or any of the programable 3 or 4 head dosing pumps like the jeboa, bubble magnus, of GHL. The higher the quality the pump and motor, the better this will work. The benefit here, is that any error between the two pumps we can correct for, meaning we don’t have to mix our salt to a different value. The down side is that the errors between the 2 pumps will generally be greater, and we will see drift of the pumps, meaning that the amount the pumps pump will change between each other. There is also a greater chance of a motor or pump head failing and pumping little or no water. Basically, we can achieve greater accuracy, but it comes at the cost of maintenance in the form of calibrating the dosing pumps. I do not generally recommend going in this direction, as the pumps are generally lower quality and more expensive than a good, used, dual head pump.

So dual head dosing pumps, a great option for those who have limited space, would like more continuous water changes, and those looking for reliability. On the downside we have to watch out for salinity drift due to differences in pumping volume.
 

Tahoe61

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Thanks for the detailed instruction. :) Great write up.

@mdbannister
 

Bramzor

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Nice video.

I'm considering building an AWC by modifying https://www.aliexpress.com/item/32948192564.html so it will have 2 heads on one motor to increase the probability of having an even water change. Its a 0-400ml dosing pump and it would have to pump saltwater from 2 rooms away and push the used water out over the same distance.
I wonder if it would be possible to calibrate the pumps if the water change is not even using a valve on one of the tubes to restrict flow on only that line.
Also wonder if I should use the RO 1/4" tubing or if there would be a big flow difference compared to the more expensive 3/8" RO tube. Could be that it does not make any difference because of how the pumps work but not sure.
 
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