Another dumb question for you - just wondering which type of solenoid is best / safest. Do people use one that is normally closed or one that is normally open? I see both for sale and can see advantages with both but not sure which is better overall.

Thanks.

Open=> gas flows, closed, it does not.

So when the electric is "on" (say in combination with the lights), the solenoid is "open".

When it's off, the solenoid shuts off.

That's typically what is used.........and set up for controllers, and other set ups.

Regards,
Tom Barr

Normally open would be a very bad idea, think of the scenario of power failure.
The co2 would be on as long as the power failure would last, if it were long it's pretty sure your fish would die.
As i see it normally closed does not have any disadvantages as long as you buy a solenoid which is made to be on for 100%, some have smaller duty cycles and could burn if they are open long times.
I also thik all regulating electronics that you can buy is made for this type NC.

Great, thanks guys.

That's one part of my system resolved (now just have to source it and the rest, lol).

I too would be nervous with one that allowed the gas to flow uncontrolled during a power failure.

Those of us who don't use pH controllers let the gas flow all the time anyway, except at night. The safest way to use the controller is to set the CO2 flow so that it is just a bit above what the tank needs, then let the controller shut it off only occasionally. Then if either the controller or the solenoid fails you don't have a fish disaster.

I agree that this is the safest for the fish, but for the plant it could be bad because if the plant load grows you dont have head room for the increasing load and your tank will be short of co2.

As I figure it, most of the CO2 we inject into the tank escapes from the water surface over time. So, a given bubble rate will support quite a lot more plant mass than is there when we set the rate. In any case, it is essential to monitor CO2 ppm periodically - every few days - if there are big changes going on in the tank. One advantage of CO2 mist is that a lot of the CO2 doesn't ever dissolve into the water, but just floats thru the water until it encounters a leaf or the water surface. This has to be much more stable in terms of ppm of CO2 in the water.

I am not to sure about this, i have a high light rich planted tank and another tank with just a few plants and normal light, the amount of co2 which is added to them to hold the same ppm are very different, of course there are other differences as well but still there is a major difference in bubble rate and on time of the solenoids.


In my case i almost never check the rate, i have it high enough to add the needed co2 in less than 30 minutes (which does not say much), then i know there will always be enough.


The disadvantage of it is (in ph measure terms of speaking), its harder because it is not dissolved as much and harder to measure the level of available co2.