What are your tap water's chlorine levels? Yeast and chlorine are no better off then fish and chlorine. Tank water is best used in fermentations, IME.
I have a bucket of tank water I used already hit with Prime. Nothing goes near my tank that has been near my faucet lol I learned that lesson last time so I keep a 5 gal bucket of primed water for topping off evaporation, cleaning filters, and used it in this CO2 device
I don't want to discourage you. DIY is in your blood. I can see that. If done right this makes for a great fermentation project. And adding CO2 is a great idea. Yeast produce a good amount of CO2 and the ones we use do it when deprived of oxygen. They are contained and allowed to gas off into our planted tanks. What could be better? Well, we know the answer to that and a 75 gallon tank will require a lot of effort on your part.
Yes I have always been able to invent ways around stuff dad was a big inventor when it came to fixing stuff around the farm, However I do most of my Stuff just to get by til I can afford to replace iot with proper stuff. I never buy used other than house or car it is always new as I dont want other peoples problems. So I make do while I save up to purchase.
Mostly, the yeast are used to run CO2 generators. It helps a great deal if we can keep their CO2 output as consistent as is posable - fluctuating CO2 levels are not the ideal. Depending on changing growth and reproduction rates, yeast strains, colony strength, temperature and available Oxygen, yeast can produce optimal CO2 levels - for about 20 days. Taste characteristics at this early date, should be somewhat dry. :02.47-tranquillity:
Well with the plants I will be using the CO2 isnt really anything more than a slight suppliment for them I am not really using it because I will have plants that require it but more as a booster. I will change one bottle im abt 5 days and 5 later change the other so that each week for a bit I have a constant. this is mainly to boost some of my plants to get them started then prob wont really use it after that, and will use other stuff to help them (i could be doing it all Bass Ackwards etc but I am a mad scientist experimenting in my Evil Lab right now
I had success growing plants in a 20gal tank using a 1 gallon CO2 generator. How to get the CO2 dissolved in water? That was and is the real question. No need for expensive, high pressure valves and parts. Here are, the throw away if you can't clean them parts. Cheap pumps with a reaction chamber will do and are the best option I found for the 20 gallon tank I had.
I have mine feeding directly into the bottom of My Ehim 2217 canister filter and will let my canister diffuse it into the water efficiently
Your DIY model in theory, might be better suited to your tank's 75 gallons if you make two of the 6 liter model and have diffusers at each end of the tank.
If you haven't seen it, here is as comprehensive an article on DIY CO2 as I've seen. John LeVasseur's, "A Treatise on DIY CO2 Systems for Freshwater-Planted Aquaria."
http://www.qsl.net/w2wdx/aquaria/diyco2.html
One of the better pump DIY diffuser models is found here at the Barr Report,
http://www.barrreport.com/showthread.php/41-DIY-internal-Reactor-great-for-Yeast-CO2-users