As I've mentioned before, this is my jam. We're coming to this idea from different directions though. You are starting high energy and trying to cut back, while I started out going for the most humble, bomb proof low lech tank possible and am working my way up. The mentality is a little different, probably. I've got several tanks, but this is my highest light one yesterday:
It's still a work in progress, but I'm happy to talk about my methods and what I have learned.
First, a lot of the same principles apply to all tanks. Most of the algae causes and solutions are exactly the same with or without CO2 supplementation. Healthy plant mass is the key to ward off algae, as is finding balance between lighting, the plants, and nutrients. Obviously I can't adjust my CO2, but all the other techniques are on the board to be deployed as needed. Maintenance is similar to a high tech tank - I clean the top of the substrate, remove old and damaged leaves, scrape the front glass if I need to, etc., but because growth is slower, there’s less to do overall. And there’s less of a penalty for a period of neglect. I find that a weekly big water change is always beneficial and stick to that schedule most of the time, but in my most stable tanks I can and do go a month without much worry.
As for factors that are important to medium energy specifically, the biggest one is probably the substrate, specifically an active substrate with organic material. (If someone has been pulling it off in inert sand I’d love to see it, but I think it puts you at a disadvantage at a minimum.) As I see it, a functioning substrate is the foundation for all other success in the tank. It’s the driver of available CO2, provides the majority of the plant nutrients, and houses the majority of the bacteria. I know that you can just feed from the water column, but I’ve had better luck keeping the water column lean and taking advantage of all the specialized adaptations found in the roots.
It’s tricky though, because you need to have the right amount of organics - too little and growth is poor, and too much and algae becomes a menace. I know Sudipta recommends the original Amazonia and I assume that’s good advice, but personally I had a great experience using a raised bed mix mixed with a little of my iron-rich clay I dug out of my side yard. The organic matter in the mix is mostly composted pine and sphagnum moss, which are pretty slow to break down and I never had an unmanageable flood of nutrients right at the beginning that many people experience. And while I initially worried about the soil becoming depleted, my oldest tank is an absolute rock 4.5 years in, churning out clean growth with ease and managing the same species as the tank above, just with less color and sometimes different growth patterns due to having less light. (I am a bit baffled about this honestly, but the proof is in the puddling.)
The next most important factor is, unfortunately, patience. I plan on a new tank taking a year to find its feet. I know, that’s a long time! But I have found I need to include fast growing species and floating plants initially, and then as the scape grows in I can take them out and introduce more sensitive stuff. (I can’t even keep floating plants alive in the long term - the water column is too lean.) It just takes a long time for the tank to mature, which I assume is largely due to the microbiome not being established, hindering endogenous CO2 production, and not yet having healthy plant mass, enabling algae. This is another aspect I don’t fully understand the mechanics of, but experience has shown me that introducing novel species is way harder in a new tank and it’s better to just wait. I also start with a bit lower lighting, so the plant colors are not as vibrant until I can crank it up. I do get a bit jealous when I see a high tech tank that looks full and luscious 6 weeks after planting, but I haven’t been able to pull that off. On the other hand, I’ve had lots of problems that just go away on their own with time, which is pretty great too.
I think it pays to do a lot of research on plant selection. I know there's a lot of emphasis in some circles on growing plants that are seen as difficult or demanding, but I would dropkick that mentality into the sun for this kind of setup. It is mind poison, truly. You need to pick plants because you like how they look and you think you can grow them successfully! Go back and look at less demanding plants and look at them with fresh eyes and see what you respond to. It's not all green! Tiger lotus and Ludwigia 'Super Red' are classics for a reason. Rotala 'Blood Red' is fast coming up the ranks for good reason IMO. Like I said before, you need easy plants to help get things going and once then you can branch out once everything is growing well. I know you love stem plants
@Art, but I would encourage you to consider bulb and rosette plants. There are a ton of crypts with interesting colors and textures that are absolute workhorses in low tech tanks. Once they are fully grown in (which, again, requires patience), crypts cannot be overrated IMO. There are colorful, carefree Echinodorus and striking Aponogeton. Buce can color up nicely, but that’s another waiting game.
There are a million other odds and ends that I believe help, but I don’t really know how much because I haven’t experimented with changing them. For example, I run my tanks in the lower 70s as a matter of course. I understand this increases dissolved oxygen levels compared to higher temperatures and other people find it makes a big difference. My tap water is soft and again, I hear that’s great, but it’s all I know. I remineralize to ~4 dGH because I have shrimp.
There are other factors I’m more ambivalent about. Flow and filtration, for instance - I think you need some, but I know that it’s that big of a deal. "Flow is king" seems like a bit much. I have a fertilizer strategy that is working for me (lean water column, rich substrate) but I am not a fertilizer micromanager by any stretch. I couldn’t be one if I wanted to - between the soil, my livestock waste and my tap water there are too many unquantified inputs to try to impose ratios or what have you. Other techniques may work fine too, I’m just disinterested in investigating. I’ve done a dry start and a dark start and don’t know that it helped much in the initial setup period. I don't have much to say about lighting other than if you don't have enough PAR your colors won't be as good. I don't even know what PAR I'm running anyway. The point is, I am not really focused on any of these things. Maybe I will come to realize they are super important down the road.
On a final note, I have one big factor working against me - my ph is just south of 7 and thus am not maximizing my co2 availability like I would if it was under 6. I have considered fixing this with strong acids, but have decided that I am too lazy and risk adverse, so I am just accepting it as is. Maybe later I will be tempted to mess with it, who knows.
