I built this for my current 90G. After testing all aspects of the system, I decided against using it on my 300G. Many of the aspects of this system were designed to allow the use of cheap paristaltic pumps (read Aquamedic). For the CWC system on the 300G, I decided that it was more effective to simply invest in a high quality paristaltic pump and the whole loop thing wasn't needed anymore. I may pull this post down at some point, but for now you can take a look if you are interested.
Continuous Water Change System
“Continuous water changes, despite their name, are not necessarily performed every minute of every day. The distinguishing feature of these changes is that water is added at the same time that it is removed. The actual rate of addition can be high or low. Reef aquarists (myself included) most often perform these types of water changes with two matched pumps, one that removes the old water and one that adds the new water.” -
Randy Holmes Fraley
The plan is to build a continuous water change system that changes approximately 30% of the total system volume every month. Estimating the total water volume at 400 gallons, then 30% of this is 120 gallons. Based on a 30 day cycle, this is 4 gallons every day.
There are a number of design challenges that need to be overcome for the system to be successful.
• Proximity to tank – The holding tanks are fairly large and in my situation must be located in the water room.
• Drain – Access to the drain is in the water room.
• Incorporate chiller into system.
• Able to operate unattended for a minimum of 30 days.
In order for the system to run for 30 days without any intervention, the reservoir has to be at least 160 gallons.
The basic premise is to build a closed loop between the tank and the water room. Along the loop, there will be several key components.
• A tap for a peristaltic pump to add water from a reservoir of premixed saltwater.
• A tap for a peristaltic pump to remove water into a drain.
• A Chiller.
It is assumed that the peristaltic pumps will add and subtract water from the system at exactly the same rate (matched pumps). However, this assumption needs to be tested and verified. If the system is not calibrated perfectly, the risk is that the salinity will either rise or fall over time. (The water level in the tank is unlikely to be affected as the ATO system will ensure that the water level is constant.) If the pumps are not perfectly synchronized, there are several easy solutions including running one pump longer than the other, or adjusting the salinity of the new saltwater to compensate for the calibration error. In any event, the rate of change is so small (4 gallons per day into a 400 gallon system = 1% change) that any drift in the system should be easily detectable before the parameters wander too far.
In addition to the basic loop, there will also be a system in place for larger “batch” water changes. This system will be based on a series of valves that really just enable two additional features of the loop.
1. Enable water to exit the loop directly by way of the drain.
2. Enable new saltwater to be pumped into the loop from the reservoir.
Plumbing
The plumbing schematic helps to illustrate the overall flexibility built into the system.
All of the components are connected to unions so that they are both serviceable and replaceable.
Normal Operation:
* Open Valves – A,B,D,E,F,G,H
* Closed Valves – C,I
Batch Fill:
* Open Valves – D,E,F,G,I
* Closed Valves – B,C,H
* Doesn’t Matter – A
* Change from Normal - Close B,H - Open I
Batch Drain:
* Open Valves – A,B,C
* Closed Valves – D,I
* Doesn’t Matter – E,F,G,H
* Change from Normal - Close D, Open C
The Chiller
One of the secondary design goals of this system was to get the chiller as far away from the tank as possible. This is because the chiller is loud when running and produces a lot of hot air. Having the chiller in the water room should solve these problems. The only drawback that I see of including the chiller in the loop is the additional head pressure that it adds. The manufacturer estimates the head pressure through the chiller at 4’.
The Reservoir - Heater and UV Sterilizer
The reservoir mixing loop has both a heater and UV Sterilizer.
The heater will not normally be activated. With the extremely slow introduction of the new saltwater, I am not concerned about matching the tank temperature. While I expect it to be inconsequential, I would prefer the water to be cold to help with cooling. If I plan to do a batch water change, I will activate the heater and allow the temperature to adjust before doing the WC.
The UV Sterilizer will be on whenever the mixing pump is on (and valve H is open).
The Peristaltic Dosing Pumps
I bought the
Aqua Medic Reef Doser Quad - Dosing Pump for another project that I didn't end up building. As a result, I have 4 peristaltic dosing pumps sitting on a shelf.
Initially, I really didn’t like the Reef Doser Quad. The controller has some major limitations that make the pumps unusable in most situations. For example, in the event of a power failure, all programming is lost. Furthermore, there is no concept of actual time – everything is programmed based on elapsed time. Needless to say, I was disappointed with the purchase.
In hopes of finding an easy way to control these dosing pumps with my controller, I took them apart and found them to be easily moddable. Firstly, the motor runs on standard AC power. Secondly, all of the dosing pumps are easily detachable from one another. After tracing the wires, it was pretty easy to hook up the motors to a standard PC power cord which can then be connected to a timer or controller. The original controller basically went in the garbage.
These pumps are rated for (1.5L/Hour or 0.4GPH). To achieve a daily exchange of 4 gallons, the pumps have to run for 10 hours.
To minimize any stress to the system, I will stagger this throughout the day. The cycle will be 1 hour on followed by 1 hour off for 10 full cycles. The final cycle will be 4 hours off to complete the day. (24 hours = 4 gallons)
Challenges
As with any system, there are some unknown factors. Some of the questions that I have are:
• The loop is pressurized. I’m unsure what effect this will have on flow rate through the peristaltic pump?
Limitations
• Heat - The pump will introduce heat into the system.
• Energy – The pump will consume energy
• Maintenance – Cleaning the loop will be difficult due to the length. I will replace the spaflex tubing once every year or so.