So you've encapsulated everything I've been saying. Everyone led me to something that is more difficult to do when I was already failing at the "easier" end of the spectrum. And the encouragement to keep going..to go further.. that if you just become more high-tech, become more knowledgeable, that somehow, I'll get it. True perhaps, but at what price. I didn't want a PhD in aquatic ecosystems. I just wanted a nice aquarium. It has never been my goal to have a show tank by the way. I've come to realize that your last statement is exactly it and it wasn't what I was shooting for at all. So, I've come full circle. Now what?
I know that I might be one of those giving "the only solution" here, but bear with me, and dont feel that you need to follow this path.
I have had pretty good success with capped soil. That is a low tech starting point, that still can benefit from hi-tech.
I have a 250 Liter running with it, that is lush and nice. It did have some infusoria, but that was because I (over)fertilized it.
An even better example is a tank I set up at my ex. place for my son. That is a 120L.
At the bottom i put a small layer of cheap flower-soil, a litle clay and caped it with sand.
Then I planted a few cryptocorynes, put some java moss and java ferns on a couple of small roots. I also added some fast frowing plants that take nutrients from the water aswell as the substrate.
That tank has been working nicely from day one. There was some algae at the start, but they dissapeared after a month or so. There have also been a litle black alga on some of the plants, but they seem to dissapear as the plant have been cut back.
In the tank there are some snails (pond snails), 10-15 endlers guppy with a lot of fryes, 5 Aspidoras + 3 small ones. Not to mention a group of Cherry shrimp. Just added a ram cichlid to hopefully reduce the number of guppy fryes(will add another one later).
BTW: I think that snails and shrimps are realy good for a tank, as they will glean up uneaten food and algae as they arrive. At the same time, they produce very little waste.
The nice thing with this setup, is that you seperate the nutrition in the substrate from the water colum, so you only need to get the water collum sorted. The java moss and ferns will take some of the nutrition, while the fast growing plants will take the rest. For rooting plants, you can more or less add whatewer you want, as long as it does not dissplace the plants that take nutritions from the water.
Unless you have a lot of fish or feed them pretty hard or have eccess nutritions in your tap-water. This should work out wery nice with very little hassle.
If you want to add CO2 and fertilizers, I suggest that you wait untill the initial algae bloom is over, and the tank is setteled. Then you may add a little CO2 if you want, and slowly bring it up. You should not add nutrients before you start so see that it's needed, and always less than prescribed at the package. (Start with 1/10 th)
As a final note - I tend to take a easy-does-it route, slow changes over time is better than abrubt changes, and if there are a few algae - I just wait them out. Unless its green water, I just feed less and wait a couple of weeks. Most times this is enough.