Unfortunately the cheapest (start up costs) and easiest method of CO2
injection are not the same. The most inexpensive method of CO2
injection is DIY CO2
, but the easiest is Pressurized CO2
Dry Ferts are definately the least expensive way to go with Ferts, although you may want to go with one of the liquid ones for Micro/Trace Ferts.
KNO3 (Nitrate and some Potassium)
CSM+B, or Flourish Comprehensive, or Tropica Plant Nutrition (Micro/Trace Ferts)
Here are a couple of possible sources for Dry Ferts.
Rex Grigg's Dry Ferts
Aquarium Plant Food Store
(used to be owned by Greg Watson, but recently sold)
For a 29 gallon tank you would be looking at closer to three 2 Liter bottles. You can simply use T connectors to join their production and then use a single method of diffusion. Make sure to rotate when you change out the mix in each of the bottles as DIY CO2
is variable by nature and stagger the start times helps to even out the production. (ie change out one bottle every 5-7 days)
While Flourish Excel is a good source of carbon (CO2
is also a source of carbon) it's not quite as good as nice steady levels of CO2
and can get expensive the larger the tank that it's being used on. It also has to be used with caution in tanks that have Anacharis and Vals as they are sensitive to it. It can be used by itself or in combination with CO2
Don't forget to look at the Macro Fertilizers (Nitrate, Phosphate, and Potassium) as these are generally more important than the Trace Ferts. If you're short on any of these (which I believe from your other thread you were as Nitrates were bottoming out) then dosing Traces isn't going to help much until you get those straightened out first.