some people use bubble counters and try to slow the bubble rate witha controll valve or clip to like 1 or 2 bubbles per second. with a diy bottle the first day it starts kicking in, bubbles will be way faster than that. you will notice a ph change at night the co2 will drop your ph a bit and should go back close to normal during the Day.
here as a friend put it to me in a Email once.
Running an airstone will help keep CO2 levels the same as what is in the air around the tank (or rather, the pump). Bubbles and surface agitation create more surface area for gas exchange, which keeps the dissolved gas at the same concentrations as the surrounding air. This works well for low-light plants and somewhat well for mid-light plants, but usually doesn't provide enough CO2 for rapid growth of mid-light or high-light plants.
This is why surface agitation is actually bad if you have CO2 injection, as the gas exchange tries to even things out, dropping the CO2 to normal atmospheric levels.
I disagree that pH shift due to CO2 is inconsequential. pH shift is pH shift, and can be harmful to fish. kH shift is a matter of hardness, not pH, and is a different thing entirely (though it does limit the pH, generally). Many aquarium fish will tolerate such a shift, but some are extremely sensitive to it, and will not do well with a daily rollercoaster like that. If using injected CO2, it is a good idea to know the fish you are working with and whether or not they are tolerant of changes in pH.
I use a glass/ceramic diffuser to create fine co2 bubbles in my tank. Using the DIY method (2 liter bottle, 2 cups of sugar, 1/8 tsp of baking soda, about 1.5 liters of water and 1 tbsp yeast) the worst blow-out I've had has done little more than create a small popping sound -- nothing major like a BP spill.. I use a check valve so in case there is a blow-out (of the air hose attached to the pressurized 2 liter bottle) no aquarium water leaks out of the tank and on to my floors, as a result of siphoning..
A good fish store near you should sell them. And like all things related to the DIY co2 method, they're cheap. I also bought two online. One I bought from Hong Kong; the other came to me via Registered Mail from Singapore. Each cost something like $5 or $6 w/free shipping. If no store near you sells them, you can order them online through ebay. Search for 'co2 diffusers' and you're bound to get a long list. The wait time for mail deliveries however is something like 2 weeks.
I run DIY on all my 10s. You could do pressurized if you wanted to spend the extra money on it. If so, I would look into the paint ball tanks. May be a better fit for the smaller tank.
I haven't had any issues with any of my bottles and I run the nano ceramic diffusers on all of them.
As for DIY diffusers...you have a couple of options but won't yield the same results as a regular diffuser. Those being chop sticks and cigarette filters (I haven't used these so can't comment on them). For the cig filters, only use the ones that you would buy from a place that you can roll your own.
Or...check with your LFS. Some of them will carry limewood diffusers. These work well too.
You could do the Hagen CO2 Natural Plant System as Big Dog mentioned....but....I would recommend doing the DIY CO2. More cost effective and lasts longer. The Hagan could be a good starter if you're just getting into it.
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