Just want to share some advices about the CO2
reactor with a backing soda / citric acid.
This reactor based on the classical "Kipp's apparatus" was initially developed by the group of Russian aquarist and modified by Russian aquarist SLAVKA. Some time ago, chinese manufacturers started to make this system and now you can found some modifications at eBay or Amazon, like this one
which I using now.
Unfortunately, all these system made with simplified general scheme and instructions, and have some problems with a stability. In my experience, the pressure in the chinese original system was growing permanently; this is not good. Also, starting of the system is a very annoying process.
So, I make some modifications of this system, based on the original SLAVKA's scheme, but with some my own modifications to improve stability and made system initialisation easiest and more predictable.
The scheme is attached.
It is very important to place the acid output to a bottom of the bottle, under the soda layer, because the product of reaction is lighter that soda solution, and if you will just drop the acid from the top, you will have a very unpredictable and unstable reaction.
Using of a needles is important to control of acid dosing, and I moved the 3-way connector to a bottom for same reason.
To start the system, I using the car air pump. Just connect it to the system's output, and make a pressure about 1.5 atm. Close the regulator valve, and connect the system to your tank. You can use a solenoid valve with this system without any problem.
The proper reactives dosage is:
Citric acid: 150g of an acid + 200ml of a pure water (acid should be totally dissolved)
Backing soda: 200g of a soda + just SOME water (soda will not be dissolved, it is OK. You need to add water just to cover a soda and make a little water's layer over).
For sure, you may use more reactives, for example 300g of acid and 400g of soda etc.
With my experience, this system working with a great stability and allow high loading of reactives for a long-time working. My last loading (300g of the acid and 400g of the soda) still working for my 75G tank, with control via PH4 DropChecker, more of 3 weeks for now and still working, even with a 24-hour diffusion (my solenoid valve was broken and it was removed from the system, unfortunately). The pressure is VERY stable. Reaction is very consystent.
Anyway, this system is much more predictable than any kind of bio-reactors, and much less expensive than any canister system