After installing the scale on the tank and a couple weeksí worth of taking notes, some interesting thoughts have come up. When posting or discussing dosing rates, why not list CO2 dosing in ppm? If one has a scale for the CO2 tank, itís simple to do.
The advantage with listing ppm are:
1. It correlates with how weíre listing other dosing parameters which is in ppm.
2. Itís easy to do, all one needs is a scale to weight the CO2 and regulator.
3. Itís more accurate of listing CO2 usage than another method Iím aware of. One method is via bubbles per minute, but this doesnít represent an accurate number because the amount of CO2 in an bubble varies with size and pressure, and thereís no practical way of measuring the size of an bubble, nor very few are measuring the pressure with accurate gauges. Another method is measuring by flow rates, which is also inaccurate also because of the combined inaccuracies of pressure gauges and flow meters, plus thereís conversion formulas due to pressure and temperature and calculations required to covert to STP as a common baseline. The other issue with flow rates is itís doesnít provide meaningful information. Itís like saying Iím dosing 2 teaspoons of KNO3 to my tank; thereís really not much you can do with this information unless one knows the tank size. Listing dosing rates in ppm tells one whatís being dosed regardless of tank size.
The equation for determining ppm is CO2 ppm = (grams used/grams water in system) x 1,000,000. The 1,000,000 is used to convert the value to ppm. Thereís 3785.41 grams of water per 1 gallon of water, so if youíre used to dealing in gallons the equation is now:
CO2 hourly ppm = [(grams CO2 used per hour/(3785.41 x system gallons)] x 1,000,000.
This equation can be further simplified by dividing 1,000,000 by 3785.41 as follows:
CO2 hourly ppm = (grams used per hour x 264.17)/system gallons.
Over the past couple of weeks my average CO2 hourly dosing rate is 32. ppm. My lights and CO2 are on 6 hrs/day so my daily dosing rate is 192 ppm. I donít believe we should be listing daily dosing rates as itís dependent on how long folks are running their CO2 system, instead we should be listing the ppm hourly rate.
Example Calculation based on my tank: Over a 13 day period the amount of grams used was 570 grams. CO2 flow is on for 6 hours per day, so grams/hr would be:
CO2 grams used/Hour = (570 grams/13 Days)/6 Hours per day = 7.3 grams/hour.
CO2 Hourly ppm = (7.3 x 264.17)/60 = 32 ppm
For determining the amount of grams used, I weighed the tank prior to CO2 coming on on the first day, and then weighed the tank just after CO2 went off on the last day. I did this over a 13 day period, and then took the average. This is more accurate as itís taking the average over a length of time. Typically, the scales being used will have drift; theyíre not high accuracy due to the low costs, but taking the value over an extended period gave me better data. For more accurate and consistent readings, I found it helps to center the CO2 tank on the scale.
There are some disadvantages. One has to purchase a scale. But scales are not expensive, the one Iím currently using is less than $40. If one happens to have a fish scale, this will work also. Most of these scales will have some inaccuracies. Iíve notice that around 10% of the time the scale may not register a change for an hour, but the next hours that changes may be doubled. Or a couple of days the grams used is very high or very low. But by taking the averages over longer periods in our calcs negates these day to day oddities.
One advantage Iíve notice with using a scale is itís easy to determine when a CO2 tank will be empty. To do this youíll need to know what the tank weighs empty with the regulator attached. If you know what the daily consumptions of CO2 is in grams, the current tank/regulator weight, and the empty weight then itís easy to calculate how many days are remaining in the tank. Trying to estimate using the pressure on the low pressure port of the regulator has never been accurate for me, itís sort of hit or miss.
If youíre thinking about purchasing a scale, make sure it has the capability of providing a live, continuous reading. What this means is the scale continuously shows the tank weight. If not, itíll be a hassle. As an example, some scales have an auto-off function mode that turns off the scale after two minutes. What happens is when you turn it on, youíll most likely have to remove the tank, wait for the scale to auto-calibrate and show a reading of zero, and then re-set the tank on the scale to obtain a reading. After two minutes when the unit shuts off, youíll have to start the whole process over. Having to remove the tank and replace it on the scale is a big headache. Most likely if the scale is battery operated only itíll have an auto shutoff function. Now the bad thing is I donít see when the manufactures list or show if the scale reads continuously in their product literature. The Smart Weight scale I purchased has continuous reading with the unit is plugged in to a receptacle via an AC/DC adapter, but it wonít do this if itís on battery power only.
Also, if one is purchasing a scale make sure it can read in Kg. Most digital scales can read output in both metric and imperial scales, but weights in metric are much easier to work with as opposed to imperial units.
If anyone is still awake and has actually read this, please provide your thoughts. Thanks!