This post is part 2 of 2 dealing with water changes. This post may be somewhat long, but for anyone setting up a similar system, hopefully it is interesting.
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
Water Changes in Large Tanks
I’m sure that almost everyone does water changes on their tanks, or at least wishes they could find the motivation. The number that I’ve heard most often is 30% monthly. The diligent hobbyist tends to achieve this by performing weekly changes of 7-10% of the total system volume. There is lots of literature that promotes this and most people generally accept it as a requirement.
Water changes in large tanks seem to be thought of slightly differently. The bigger the tank, the harder it is to keep up with 30% monthly water changes. It may be that the overall benefit to the system also changes. Many large public and commercial tanks have such efficient filtration that water changes are rarely required. Calcium and other trace elements can be supplemented and there are other more effective means of nutrient export.
A good example of this is Inland Aquatics who claim to have 40,000 gallons of water and change only 5% annually.
* Over time I may experiment with reducing the volume of water that is exchanged every day. With a new tank, I personally feel that water changes will be an important part of maintaining overall stability. Once the tank has matured, the cost may start to outweigh the benefits.
System Goals
Basically, I never want to do another water change again. There’s nothing stopping me from siphoning detritus or doing emergency water changes, but the week to week changes that are typically a never ending part of this hobby just don’t work for me.
Total System Water Volume = 300 Gallons (1,136 Liters)
Percent Water Change = 33% Monthly
Total Monthly Change = 100 Gallons (379 Liters)
Total Daily Change = 3.33 Gallons (12.62 Liters)
The system can run unattended for 60 days. Realistically, I will top up the reservoirs and ensure everything is calibrated once a month, but it’s nice to have extra time as needed.
• Simple is best
Water Storage
There has been some debate as to whether it is reasonable to store saltwater for extended periods of time. I am confident that if you have a clean vessel suitable for storing potable water and no contaminates are introduced that it can effectively be stored indefinitely.
The dimensions of this loaf tank are 58"Lx29"Wx37"H. It was made by paddleplastics -
www.paddleplastics.com - I picked it up in Crossfield from Promould: 403-946-9920
The tank comes with a mainway and a bulkhead that can be installed at the time of purchase. I had Promould put the mainway on, but I put the bulkheads on myself. I installed the bulkheads on the bottom of the tank to allow maximum drainage.
Note: It’s somewhat important to mix the saltwater in a separate tank from the one used for ongoing storage. From observation, it can be seen that the mixing tank gets dirty from particles settling out of the newly mixed saltwater. By allowing this to happen in the mixing tank before transferring to the storage tank, very little contamination is transferred. My storage tank stays very clean whereas my mixing tank needs to be cleaned somewhat regularly.
Peristaltic Pumps and System Pressure
Even high quality peristaltic pumps are incredibly sensitive to changes in pressure at both the intake and the outtake. A reservoir slowly draining will cause a pressure variance at the intake of the pump as a factor of the water volume remaining in the reservoir. As the reservoir drains, pressure will decrease and the rate of flow through the pump will decrease.
To overcome this characteristic of peristaltic pumps, pressure within the system must be a constant. After considerable research into high tech solutions, I came up with a low tech solution that works perfectly. It's basically a constant pressure regulator that helps ensure the pumps stay balanced.
The water cooler can be purchased at Canadian Tire. Basically, the water enters at the top and fills the cooler to the point where the float valve shuts off the flow of water. As water is pumped out, new water from the main reservoir will replace it. There is a John Guest fiiting at the bottom of the water cooler that allows the peristaltic pump to connect at a low water point.
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I know that you can get John Guest bulkheads, but they aren't really suitable here. The trouble with these bulkheads is they are difficult to tighten without access to both sides. The trick to installing the threaded adapter is make the hole using a drill bit slightly smaller than the size of the fitting such that it threads into the plastic. I used glue on the joint to ensure a permanent seal.
SpectraPure LiterMeter III Paristaltic Pump
I've tested a number of peristaltic pumps and the
SpectraPure LiterMeter III system is, in my opion, by far the best. A good quality peristaltic pump is really important when setting up a continuous water change system or there will be a high probability of drift and/or premature system failure.
From the manufacturer’s description - "The new aquarium dosing pump is crafted from precision-machined aluminum fabricated to exacting aerospace tolerances. For example, such critical tolerances as the rollers are machined to +/-0.0005". The outer surface is polished to a mirror finish. Internal surfaces are held to a 63 micro inch finish and hard anodized to provide a durable and low-friction raceway. The pump's planetary direct drive is at an 11:1 ratio, thus providing enough torque to generate over 40 pounds of pressure. This incredible lift enables the
LiterMeter III™ to pump over 60 feet above itself at a flow rate of over 250 ml/min. It can also draw up from 25 feet below. The motor in the
LiterMeter III™ is made by a manufacturer of precision high reliability motors made to our specifications as a peristaltic drive motor. The pump is so reliable we now offer a
five year limited warranty."
Some additional features that were important to me include:
- Calibrated by volume not time
- Remote pump support
- Programming will survive a power outage
- Ability to adjust dosing volumes on each pump independently by as little as 10ml/day without recalibrating
- Automatically tracks pump run time and will beep after 300 hours
- The desired daily volume is dosed in 150 equal parts throughout the course of one day
The System
The whole system really isn't complicated at all.
Black Tubing = Water from tank heading for the drain
On the tank side, I hooked up to the first chamber in my sump. This chamber has a constant water level and as such, the pressure will always remain the same.
The water is drawn up by Pump A (built into the controller) through about 10 feet of 1/4 inch polyethylene tubing. The total vertical rise is only about 3 feet. This is then pumped through another 30 feet of tubing through the ceiling and eventually to the drain.
Red Tubing = Water from reservoir heading for the tank
The reservoir has two bulkheads installed on the bottom. One is connected to a large Panworld pump (picture not shown) which is used to agitate the water once every 4 hours. It can also be used to pump water into the main tank for larger water changes.
The second bulkhead (shown above) has a John Guest fitting which connects to the pressure regulator water cooler. The floor of the main resevoir is elevated to approximately the same hight as the float valve installed in the water cooler thus allowing the main resevoir to completely drain.
This bulkhead also has an attachment for a drain line as can be seen by the cap at the end. The plumbing for the drain is stored detached to keep it out of the way, but can be easily reconnected as needed. The drain can be used in an emergency or for periodically cleaning the loaf tank.
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The remote LiterMeter pump pulls water from the pressure regulator water cooler and pushes it back to the tank through approximately 40 feet of tubing ran through the ceiling.
One interesting observation is that the run from the reservoir to the tank seems to have considerably more resistance. The calibrated flow rate through the LiterMeter pump B is about 80% of the calibrated flow rate through Pump A.
Heating the Reservoir
Heating the reservoir is not necessary. I keep a couple of spare heaters that could be used to heat the water in the reservoir if an emergency situation arose, but because of the very small volumes of water that are added to the main display tank, there is no measurable affect on temperature.
Tuning
The LiterMeter pumps are calibrated by volume. To accomplish this, the system asks you to fill a 500ml vessel and to stop the pump when complete. Once set, the system adjusts the calculated flow rate through each pump accordingly.
I found this difficult as the output of my tubing is nowhere near the controller. To overcome this challenge, I set the pumps to run continuously and timed how long it took to fill the 500ml. I repeated the test a number of times until I had an average that was within a reasonable margin of error. When I ran the calibration routine, I simply started a stop watch at the start of the test and stopped the pump at the appropriate time.
500ml - Pump A = 2.07s
500ml - Pump B = 2.47s
Once calibrated, you can then set the run time for each pump indendantly. Everything is done in metric. The initial configuration to achieve my desired rate of water exchange is:
Pump A: 12.62 liters per day.
Pump B: 12.62 liters per day.
The only reason we really care about precise calibration is to avoid any drift in salinity.
The SG of the saltwater in the storage reservoir is 1.025
The SG of the saltwater in the tank is 1.025
If the pumps are perfectly calibrated, then the tank will stay stable at 1.025.
- If there is a calibration error causing a slow increase in salinity, then the daily volume for pump A can be increased (or pump B decreased).
- If there is a calibration error causing a slow decrease in salinity, then the daily volume for pump B can be increased (or pump A decreased).
It's a little like guessing a number between 1 and 10 where the person who knows the number answers with "higher" or "lower".
The only other consideration is evaporation of tank water and the ATO. Ideally, this would be unaffected by the water change system as the volume of water in and out of the tank is balanced. However, if the margin of error is too high, the rate of evaporation could exceed the variance or vice versa. In any event, this is unlikely and the solution would be to recalibrate the pumps.
Safety
There are a couple of scenarios that warrant additional consideration.
Pump Failure or full blockage
These pumps are quiet. Without periodically checking, a failed pump could go unnoticed for weeks. The result would be a a proportionately rapid shift in salinity.
This scenario would not be immediately evident as the ATO would maintain a constant water level.
To mitigate this requires some diligence. Operation of the pumps should be checked at a minimum of every couple of days.
* I am considering installing flow sensors on the lines and connecting them to my Apex controller. I have one already that I am not using, but also haven't tested it yet. If I can trigger an alarm based on a period of inactivity, it may solve this problem.
Calibration drift or partial blockage
This would only be detectable through measuring salinity. Any unexpected change in salinity could likely be attributed to either calibration drift or a partial blockage of one of the lines.
- When the pumps are flagged for maintainence (every 300 hours), all of the lines should be cleaned to prevent salt buildup.
- Every second servicing, all of the lines should be replaced.
- Once a month, the time it takes to fill 500ml should be recorded. If there is a variance greater than 2 or 3 seconds then the lines should be cleaned and the pumps recalibrated.
Dry Reservoir
This one is pretty easy to deal with. The reservoir is very large so simply spot checking should be sufficient. However, I also plan to install a level sensor into the pressure regulating water cooler. If the water level drops for any reason, the Apex controller can alert me.
The system is expected to run for extended periods of time without requiring any adjustments. However, it does require some monitoring to ensure that all systems are opperating as expected.