...sorry for the thread hijack, but this was just so fascinating I couldn't resist.
Friends don't let friends kill HC.
I don't think AirSong minds you hijacking.
You stated that nutrient deprivation is the biggest reason that people fail at growing HC, glosso, and riccia in non-c02 tanks.
To be clear: light AND nutrient deprivation.
I've seen that many people view low-tech, non-co2 tanks as dark, murky places that have plants with spindly growth where anubias, crypts, and java fern reign king. They are overly cautious about having extra nitrates, phosphates, and iron in the water column. And they gravitate toward plain gravel or other DIY substrates that are essentially inert and don't have good CECs (Cation Exchange Capacity).
But some are brave, and they do try to grow things like HC, hairgrass, glosso, and riccia etc. However, they apply the same low-light, nutrient thin philosophies - because that's what a low-light, non-co2 tank is... right? And when the plants eventually die off, they begin to think that such plants can only be grown with CO2 injection, high light, and heavy dosing routines.
To me, a low-light tank is this: It's a tank in which the natural, biological nutrient supply is able to keep up with the demands of the plants, and that demand is driven by the light. Nothing more, nothing less. It's a tank that relies on biology to create CO2... and these bio-chemical rates, albeit slower, are able to keep up with the plants. Surely there is a range of light intensity that works well... and how do you know what the top-end of that would be?
You can't guess this range just by making sure that you have 1-2 watts per gallon. I have disliked this rule-of-thumb ever since the first day I got into this hobby. It never made sense to me - Photosynthetic energy is what is important, not watts. I've seen people trying to grow various plants in a 20 gal tank, a gravel substrate, and a trusty bottle of Seachem Flourish; And I measured their PAR values to be around 15-25 umols/m2/s (far from 60-70 umols/m2/s). To me, it's no surprise why they are having trouble: insufficient light, and no viable nutrients (and maybe a lack of CO2 generation).
Even when they kick up the light a notch, it's not enough to fix the problem. In a non-CO2 tank, you still need CO2 and a consistent nutrient supply. To my knowledge, that CO2 comes from a robust substrate that's filled with healthy soil bacteria.
I've read so many times that you'll never see "pearling" in a low-light, non-co2 tank. This is another one of those "things" that is simply not true. The Riccia and HC in my non-CO2 tanks pearl quite a lot at the height of the day. How could this be without CO2 injection and high light? Well, it's because of a strong, healthy environment, good substrate, and sufficient photosynthetic energy. And maybe "low-light" can be higher than you previously thought... or were conditioned to think by other hobbyists.
And this is all without algae. If you really
assess your lighting, and you really
assess your nutrient supply, and you have a viable substrate, algae problems really become minimal.
However, IME I have seen riccia grow like a weed(even when tied to rock) in my high tech and low tech non-c02 tanks, but in the same tanks Hairgrass has died off and HC has failed to grow at all(even with ADA Aquasoil II and water column dosing). What is your explanation for this?
Well, to start, I would put Riccia in it's own class since it strictly derives its nutrients from the water column. Riccia is generally undemanding and if you're dosing the water column in both cases, I would expect it to do moderately well in both cases.
HC and Hairgrass, however, interact heavily with the substrate. My guess is that you can't just dose the water column and expect these plants to ignore the biology in their root system. Question: In the non-co2 tank, is the substrate able to generate the kind of bio-chemical activity that's needed to support the rooted plants? Sure, it's "ADA AQUASOIL
", but how do you KNOW what it's capable of? What's it's CEC? What is the ratio between sand/silt/clay? How rich is it? What were your PAR values?
I know you don't have a PAR meter. I'm just saying that these are the things you CAN know and remove them from the "variable" list. Personally, if I really wanted to use ADA's Aquasoil, I'd pay the $50 and send it off to a lab to have it analyzed.
That's where I'd start: Determine your photosynthetic energy, and provide a substrate of known quality and content. Only then can you begin to say anything about the success or failure of a particular plant.
I have reservations about shining too intense light on a tank. Even experimenting with a 10 gallon where c02 tested ideal, water parameters were ideal, fert dosing was ideal, and even plant growth was explosive with only 30 watts fluorescent lighting(6500K daylight) that tank was literally raped by just about every algae imaginable. BGA, followed by black brush, followed by clado, and even green dust algae. The single biggest change that resulted in the algae disappearing was a reduction in light intensity from 30 watts total to 20 watts(6500K daylight)
Here again: phrases like "too intense", "only 30 watts", "30 watts total to 20 watts"... they are all ambiguous. They say nothing about actual photosynthetic energy that you are supplying. Small tanks like 10gal, 5gal, etc are tricky because it's so easy to screw up the light, either high or low. If anything, this is what I wanted to illustrate with the slides I created earlier in this thread. Overall they show how a simple change in the distance and reflector type can make huge differences in the photosynthetic energy. And if you don't know what you've got, it's setting the stage for failure (or algae, if you equate the two).
Also, another factor is the life-cycle of the tank. In my experience with using a soil substrate, all new tanks experience some form of algae as the bio-chemical processes are kickstarted after you set it up. This period can last several months. But it goes away as the plants take hold and the substrate kicks into high gear.
If you KNOW that the photosynthetic energy of your lighting is in a good range, and you KNOW that you have a robust substrate, then you can have some confidence in allowing algae to move through it's life cycle without trying to fight it.
But if you don't KNOW those things, you may be consistently supplying an environment that benefits algae and not plants. And then it will never go away. You'll be scraping and removing until the end of your days.
Just my thoughts.