Having had a reactor for a number of years now and gone through all the trials and tribulations, I thought it might be helpful if I record my experiences.
There are three main things that have been a problem.
1. Getting a constant drip rate
2. Getting a constant CO2
bubble rate
3. Dealing with a suppressed pH level in the main tank
Although the various designs of reactor may be better or worse for this, it is generally true that it very difficult to achieve a constant drip rate using a normal pump. Eventually they slow down and you end up constantly have to adjust them. There are two potential solutions.
The first one, which I have not used, is to take a line off the main return pump and control the flow using a micro gate valve. The high pressure produced by the main pump makes it less susceptible to changes and the gate valve allows precise control.
The second way, which I use, is via a dosing pump, in my case a peristaltic pump. Dosing pumps are nice because they are small, do not require any clever plumbing, produce a high pressure and do not need to be primed. In the case of peristaltic pumps, all you have to do is replace the special tube regularly (monthly in the case of silicon tube).
The next problem I had was getting a reliable bubble rate. This was because I tried to save some money and bought a regulator from the local welding supply place. Sadly although it is probably fine for the rates required for welding, it was hopeless at the very slow bubble rates needed for a reactor. I bought a proper two stage unit with a needle valve and never looked back. For your information, I bought a Bioplast unit.
Because CO2 is used to lower the pH in order to dissolve the reactor media, the chances are excess CO2 comes out of the reactor. With sufficient water surface agitation and fresh air coming into the room, then you may be able to get away with it. However this proved impossible for me.
Therefore, what I have found works really well is to add a second chamber to the reactor. Unlike the main chamber, water is not recirculated, all that is needed is the outlet of the main chamber to be connected the bottom of a second tube full of reactor media.
This second chamber does not need to be anything fancy. I used an old DI column, but if you have an old canister filter that feeds in at the bottom then the greater volume would make that an ideal choice (do not turn its pump on though!). The only suggestion I would make is to use one of the more easily dissolved media in the second chamber. I use CaribSea Geo-Marine for all my media which is fairly soluble, unlike the "proper" (more pure) media like Koralith. CaribSea also do a special media called ARM which is even more soluble but its price is so much more than the standard Geo-Marine that I have not bothered.
Because you are using the CO2 more efficiently
then you may need to retune your reactor (less CO2
is needed). This method also works quite well if you reactor is undersized
for your tanks requirements.