Paul, thank you for your kind words. they are appreciated very much.
One thing I'm trying to do is find ways to build my own stuff on the cheap. The nutrients for instance. Would a piece of a multi vitamin tablet dissolved in the water make available most of the micro nutrients needed?
No. First, aquatic plants require specific nutrients (17 of them) and in specific proportions to each other. An excess of some can cause the plants to stop assimilation of another; while this is unlikely if properly dosed, the point illustrates why it is important to provide the right mix. We cannot mess with nature--what we are doing to our planet should teach us that much.
There are two methods to fertilize aquarium plants; a comprehensive complete fertilizer or mixing dry nutrients and adding those to the water. In either case, the nutrients are bought specific for this purpose, aquarium plant fertilization. Even terrestrial plant fertilizers will not work, as they contain different proportions and include some nutrients that aquatic plants have no need of, and this can induce terrible algae blooms along with poor plant growth.
I have never messed with dry nutrients, but some members here may have and can provide insight. I have always used a prepared liquid fertilizer, along with (sometimes) substrate fertilizer tabs/sticks depending upon circumstances. My present tanks are managing solely on liquid fertilizer added twice weekly; I use and recommend Seachem's Flourish Comprehensive Supplement for the Planted Aquarium
. It is the only one as far as I know that has all essential nutrients in proportion [oxygen, hydrogen and carbon are not included and no liquid fert contains these as they occur naturally in the aquarium]. In the 1990's I used Kent Freshwater Plant, but as I have been unable to track this down recently I assume it is no longer available; the Kent "Pro-Plant" line is the same manufacturer but not the same product, and I have not myself used these.
Flourish is not expensive; it takes very little, 1/2 teaspoon (2.5 ml) per 30 gallons is the dose, so in my 115g thats 1.5 teaspoons. I find twice a week (they recommend once or twice) necessary or my swords being to pale. When I used substrate sticks next to the swords, I could manage with once a week. Swords are heavy feeders. A nutrient-enriched substrate would help with swords, crypts and aponogetons, but they are very expensive by comparison to plain small gravel (which I use) and for larger tanks this is a consideration. With my 6 tanks, a 2 litre jug of Flourish lasts me several months and probably works out around $5 to $10 per month.
Regarding CO2 injection for a planted tank, would it make sense to allow a small pocket of CO2, say 50 cc or so, collect under an object that is underwater (say an overturned cocconut shell) so the water - CO2 interface gives more time for the water to dissolve the gas?
This I'm not sure about. I have never used CO2 and never will, solely because for my purposes it is totally un-necessary and an expense I cannot thus afford when it is not essential. You have seen the plant growth I have from my photos; that satisfies me perfectly. I am personally not a fan of high-tech setups because of the increased light, which I believe is detrimental to the fish. There is also the increased cost to setup and maintain--triple light means triple use of electricity, daily dose of nutrients, plus the CO2. The benefit would be faster plant growth and perhaps growing some plants I can't grow as well now. For me there is no purpose in faster plant growth; the balance in my aquaria is stable and the fish are spawning somewhat regularly, so I've no desire to tamper with that.
On the issue of CO2 dissolving in water, it is not the slowness of this but the slowness of aquatic plants to assimilate CO2 from water. This is the issue with water movement and surface disturbance, which also affects the plant's assimilation of other nutrients. Aquatic plants take 4 times longer to assimilate CO2 from water than plants do from air, so maintaining a proportionally high level of dissolved CO2 is important. At the same time, oxygen cannot be allowed to increase (the other aspect of faster water movement) since increased oxygen is detrimental because it binds with some nutrients, especially iron, which then becomes too large to be assimilated by the plants. High oxygen also prevents plants from easily assimilating other essential nutrients.