Not So Astute Observations
My most brightly lighted low tech planted tank is a 20 tall with two 14 watt daylight CFLs. From posts here on the site, I gather that I'm a little on the bright side. Nevertheless, I can't get stem plants such as wisteria and water sprite to thrive. I'm planting them in the substrate. They stay alive but, that's all. The tank has a sand substrate and is given a touch of an overdose of Flourish Comp once a week. It is fully but, not overly stocked with fish.
On the other hand, I have a little 10 gallon experiment tank that has a lighting level of probably 5000K from a single tube and receives a low level of DIY yeast / sugar recipe CO2. It also has a sand substrate and receives somewhat of an overdose of Flourish Comp once a week. The only occupants are a male betta and many snails. The stem plants all but leap out of the water in that tank.
The obvious answer is I need more CO2 in the 20; however, I'm kind of confused as to the balance issue. Why would plants receiving lower light do better in a CO2 charged tank ? My water is in the low hard range and has a high PH of 8.6.
Just looking for some ideas.
What kind of housing do you have for the 20 tall?? I am betting it doesn't have that great of reflectors in it? So my assumption would be that even with 2 14 watt CFLs you are still in lower light range. Where as I have been told a single T8 on a 10 galllon puts you into the medium range of lighting. That would explain the growth difference. I am betting even if you took the DIY Co2 out of the loop the stems would still grow fine in the 10.
CO2 has more of an impact on plant growth than light does. That's why the CO2 tank shows better growth. I could try and explain why, but I think this link from Tropica does it better than I ever could.
Co2 has alot to do with the growth I agree BWG but I am still betting the Stems will grow better in the 10 then the 20 tall without the added Co2
Possible, definitely. I don't know enough about CFLs to be able to compare them to T8s and then factor in the extra 4" of height. I honestly don't know where fishmonger's 20 gallon falls on the low, medium, or high range. I'm taking fishmonger's word that it is higher light than the 10 gallon, and so was just trying to answer the question of why stems in lower light but with CO2 would grow better than stems in higher light and without CO2. Not saying you're wrong, Boredomb, just that I was going with the facts as presented.
I suspect you are both correct.
Light first. I have two 10w Daylight 6500K CFL bulbs over my 20g tall [=regular] and the plants do fine. This is my QT for new fish, so it runs permanently but usually without any fish. I fertilize with Flourish Comp once weekly as with all tanks I have. I never have algae issues in this tank, and the plants do as well even without fish contributing organics. Now, growth is a bit slower than in the tanks with fish, but the plants do fairly well all things considered.
CO2. This mainly occurs from organics being broken down; respiration of fish, plants and bacteria produces less CO2 by far. So, without knowing the state of the substrate organics in fish mongers' tanks, and the fish load, plus his maintenance routine...it is difficult to estimate possible CO2 levels.
As for Wisteria, I cannot keep this in any tank; even in my 70g which is only 18 inches high and has two T8 tubes, it failed after several months. Now, I accept that other factors may have played into this, as I have very soft water and was not at that time using Equilibrium to raise the GH which was at less than 1 dGH. This may have been a factor too, as calcium deficiency in particular is not going to result in healthy plants.
Wisteria loves light. I've had it in every one of my tanks, but it has only worked out in two of them. Oddly, both Beta tanks =)
But when I had it in my 20g tall with just a single T8 it did grow, but slowly. However, on one side of the tank it got just a tiny bit of sunlight late in the day when the sun was nearing the horizon. The Wisteria on that side of the tank grew really well.
A 5.5g Betta tank that has a single 10W CFL is on my kitchen counter and also gets a bit of sunlight and it's a literal jungle in there with all the Wisteria and Crypts (the only two plants).
Like Byron, I have soft water (about 1 to 1.5 dGH) so I'm inclined to think there is something to natural light that gets them going. Either intensity, or spectrum. Neither tank gets direct light for more than a few minutes (less than an hour) but it seems to be enough.
I have a 37 tall tank, 24" from bottom to light fixture with low light (8 Watts of LED). I have decent luck with most anything up to medium light plants but have not tried wisteria or water sprite. I have tested the light nearness on a few stems that were barely holding their own on the bottom by moving them up onto a driftwood which raised them about 4"-5". They went from holding their own to growing nicely and holding more of their red colouring. My one stem of hygrophila is now reddening back up on the leaves at the top as it is, slowly, growing nearer the light.
While the CO2 might make a difference it may not. If the light is not adequate enough for the plants to be able to use the added CO2 then it is, at best, a wasted effort.
I'd suggest to try floating them to see if they grow faster that much closer to the light without changing anything else first.
I measured (lux app, probably not accurate but it's gives some relative idea) as much as 5,000lux at the surface, around 1500lux halfway and 700 at the bottom in open air without shading floaters. I dropped my phone in for a real test but reading it was problematic so I skipped that for now.
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