SFC CO2 tank level monitoring

[Arne]

Hello All,

how do you know how much CO2 is left in your liquid CO2 tank for SFC analyses? We are a bit puzzled here how to better control this. One idea is to have it on a scale permanently, but there are soem concerns that make that not that practical for us.

[Consumer Products Guy]

That's what we did.

[DR]

I guess you could stick one of those color change strips on the side of the tank that shows where the temp change line is. When/where it goes from liquid to gas, there's a cool spot which transmits well through the wall of the tank due to the high thermal effusivity of metal. The only other sign you will get is that when the last of the liquid CO2 converts to gas, you will have much higher than usual pressure fluctuations in the primary stage of your regulator. As long as there's any liquid CO2 in there, tank pressure should be constant.

Planted aquarium keepers refer to this as "end of tank dump" and it is the reason 2 stage regulators are heavily favored by them - when you're running low on CO2 is the most likely time for your tank to be poisoned by excess CO2 (ironic!). If you have a 2 stage regulator and your CO2 is down to gas only, a small increase in ambient temp. is far less likely to result in the death of all of your fish.

I kind of like the scale idea - just get an OLD doctor's scale, determine the weight of your new, full CO2 tank and slide the big weight over by not quite the expected weight of CO2 and order a new tank when the beam moves off the stop. IE - for a 20# tank, determine the weight and then slide the beam weight over about 18 pounds... when you've used 90% of the tank, you should hear a "clunk" when the beam moves. I don't think that system would work in my living room, however...

[Arne]

Thank you for the pointer with the color change strip - we will definitely look into that!

As to the scale - just an indication would be enough for us.

I used to have CO2 supplemented planted fish tanks as well but I used a chemical reaction/pressure based system using bicarbonate and citric acid in two connected bottles. I didn't have the funds as a grad student to get a CO2 tank setup.

[DR]

Before I went "high tech", I used fermentation (sugar, water, a little yeast in a closed bottle that vented into the aquarium).
As for monitoring CO2 levels, I use a "drop checker" and some 4dKH bicarbonate solution with a pH indicator in it. Anything above 30ppm CO2 dissolved in the water changes it from green to blue. I do this with new tanks until I get used to what the flow of CO2 looks like to maintain a reasonable level, then I remove it.
My CO2 tank is on a timer along with my lights... so not all that high of a high tech system.

[copperfoils]

I've used a scale in the past to monitor CO2 tanks. There are scales purpose built for this application, ex: https://www.wika.com/en-en/gcs_1.WIKA?

[Arne]

Thank you for the replies.

We tried an ultrasonic device but it doesn't work on our CO2 tank - it does work on the BBQ propane tank at home, however.