SODIUM THIOSULFATE DOSING AUTOMATION
So how do handle water changes? People are asking how much, how often and is flow through an option for me?. A few months back, I designed and installed an automatic sodium thiosulfate dosing system that injects city water into my pond. It’s flexibility in design enables the ponder several modes of operation. City water is input into the system at 100 PSI. A metered amount at 10 GPM of city water free from chlorine and chloramine is injected into the pond automatically. The equipment can operate based on a float switch trigger, is time based or has a setting for constant on. This means that one can adjust the make up water into a pond totally automatically and have some choices.
The float switch options allows the ponder to have a simple pond level float switch that activates the control based on actual pond level. This mode of operation is best for one that wants the minimal water usage but needs to keep the pond topped off.
Another control option allows for full on of the dosing system. This means a constant flow of 10 GPM as well as a constant sodium thiosulftae injection rate.
The mode of operation that I am currently running is time based. I trigger the system to operate once per hour every hour of the day. The duration time is set to one minute so I am delivery 10 gallons of water an hour. I do not like to drain my pond down 1,000-2,000 gallons a week and refill all in the same day. This system lets me dose on a more frequent basis and smaller amounts of water. In the end, I am changing 1680 gallons a week. And on my 12,000 gallon pond this seems like a good balance. The water is introduced on a constant bases. For this mode of operation I recommend a passive overflow system (stand pipe or overflow drain).
System Sub Components:
The sodium thiosulftae dosing automation is broken up into three main sub components. The concentrate reservoir, system control and dosing components.
This first picture shows all three of the system sub components. To the left is the concentrate reservoir (with low level detection and control). In the center is the dosing control PLC (programmable logic controller) and to the far right is the dosing assembly. All electrical components are designed with quick disconnect for ease of use and installation.
The following picture shows the mechanical dosing components assembled. Water flow is left to right. I installed a manual shut off valve on each end of the assembly and union fittings so I could remove it from my system if need be. From left to right we have a ¾ union, pressure regulator set at 70 PSI, 200 mesh filter, fixed flow control valve at 10 GPM, 115 VAC dosing solenoid valve, dosing unit, back flow check valve and finally another ¾ union.
It real simple math to determine how much concentrate to mix. I have determined that about 10 grams of sodium thiosulfate is required to eliminate both chlorine and chloramine from 1000 gallons of city water. The dosing unit is adjustable from 500:1 to 100:1 as far as the amount of concentrate it injects. The dosing unit is volume based so errors are reduced. Anyway, I have a 15 gallon concentrate reservoir. 15 gallons times 500:1 (I run the dosing system at .2%) makes 7500 gallons. So 7500 gallon divided by 1000 times 10 grams equals 75 grams of sodium thiosulftae for each 15 gallons of concentrate that will be dosed.
This picture shows the assembly installed and running.
This next pictures show the control enclosure and what's installed inside. I designed the system to have an indication lamp as well as have a selector switch input for mode of operation. This system works in either auto or hand. Auto mode doses once an hour for one minute. Hand mode will open the flow to the doing unit and keep it open indefinitely. The lamp on the front of the control enclosure will stay illuminated in auto mode, will flash slow in hand mode and will flash fast if the concentrate reaches the low level sensor. Once low level has been reached, the dosing solenoid is permanently turned off until the concentrate tank has been refilled. An Allen Bradley Pico controller is being used for this control. It’s a low cost programmable controller that programs in ladder logic. The nice thing about this unit is that all the timer set points are adjustable from the operator display. In addition, you do not need software and if you can read and understand the 285 page instruction manual, you can program it as well from the operator display and push buttons. The only other item in this control box is a 4 amp fuse, selector switch and pilot light.
Finally, this picture is a poor image of the electrical schematic that I used for wiring the system. If there is some interest in building and installing this system, you can e-mail me at koiboy@mindspring.com.
