Low light + CO2/EI? Looking for guidance - The Planted Tank Forum
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post #1 of 5 (permalink) Old 08-08-2010, 05:22 PM Thread Starter
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Low light + CO2/EI? Looking for guidance

Hello all!

I've had my first planted tank for about a year now, and it's been a great learning experience so far. I've learned a lot about lighting, algae, fertilizers, and of course getting plants to grow. On that last item, I've had no trouble - everything I've had has grown extremely well. I've really enjoyed it, but I want to try a slightly different direction. I'd like to do a darker tank for South American fish (tetras/cories) and have slower growing plants.

Here's where my tank is at right now:

- 47 gallon (36x15x20), 2 x 39W T5HO, 9 hour photo period with a 2 hour siesta in the middle;
- Eheim Pro2 filter & Aquaball powerhead;
- Presurized CO2, approx. 5 bps;
- 50% water change weekly;
- EI dry dosing (nothing fancy here - just according to the sticky thread I found on here https://www.plantedtank.net/forums/fe...-regimes_.html);
- Have had no serious algae issues for the last 6 or 7 months;
- I've had Glosso, Ludwigia, Pennywort, Pygmy Chain Swords, Aponogetons, Crypts, Java Moss, and Anubias, and everything has grown well. The only issue I've had is that everything seems to grow to monster proportions, and quickly. My fish have done fine too, with no losses.

Now, here's what I'd like to do:

- Drop my lighting down to only one 39W T5HO bulb, still with a 9 hour photo period;
- Change up my plants a bit: one or two large Echinodorus along with some E. tenellus, some Crypts, maybe some Anubias or Java Fern, as well as Java Moss. I'd like to add some floating plants too (maybe Salvinia or Amazon Frogbit).

Now, my questions are:

1. Could I still use pressurized CO2 with low light/slower growing plants? I assume this would fine if I dial it down some, but looking for opinions here.

2. How would I need to fertilize a low light/slow growth tank? Would I just scale back the basic EI method?

3. Would a single 39W T5 bulb be sufficient for my desired plants above?

4. How often would I need to do water changes if I'm no longer doing a strict EI dosing regime? Still once a week, or less since I imagine I wouldn't be using an EI methodology.

Any advice would be great. I'd like to maybe start over with a whole new set-up in October maybe, so between now and then I want to develop a clear plan of action. Any help is greatly appreciated!

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post #2 of 5 (permalink) Old 08-08-2010, 05:26 PM
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All my tanks are low light

I add a bit more PO4 than typical suggestions, and dose 2-3x a week.

Feed fish well, good current and light is pretty low, not to mention 36" away from the bottom of these tanks, all my tanks for that matter.

I'm not clear on why dosing less than full EI is no longer EI...........nor why doing less than 1x week is no longer eI or any of that.........???
It's not meant to be so rigid, never was.

Folks have not read what I have written about EI or asked me if they think this.


Some common sense should be applied.
I dose these tanks about 15ppm NO3, 5ppm PO4 3x a week.
I've breed CRS's, RCS, L014 red farowellas, Cories, have a nice pack of various tetras, catfish etc.
Some tanks go 2-4 weeks without water changes etc.

Tom Barr

Tom Barr

Last edited by plantbrain; 08-09-2010 at 02:49 AM.
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post #3 of 5 (permalink) Old 08-08-2010, 05:58 PM
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#1: Yes, and you're correct that it would be dialed down a bit due to slower consumption. But even though the input will be less, you want to maintain the same CO2 levels in the water as any other tank. Hopefully you have a drop checker to help you dial this in.

#2: Yes.

#3: Should be. I'm bad at estimating light requirements though.

#4: I would continue with weekly water changes, at least for a while until you get a feel for the new setup. Then try extending that and see what happens. And as Plantbrain said, even with these changes it's still considered EI. Call it modified EI if you want, to distinguish it from the "normal" guidelines when posting.
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post #4 of 5 (permalink) Old 08-08-2010, 09:11 PM
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I have a low light, high tech 10 gallon that's a mini version of the tank you're planning. I love it! Plants are healthy, no algae, and hardly any trimming. I do like playing with my higher light tanks, but I sometimes get sick of the "plants on steroids" effect.
If you're not planning to make the change for a few months I would suggest starting the sword(s) under your current lighting so you can grow them out more quickly. As long as you have root tabs I think they should be fine making the change to low light.
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post #5 of 5 (permalink) Old 08-09-2010, 07:32 PM Thread Starter
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Thanks everyone for your replies. And Tom, thank you for the link to your article; it definitely helps. You illuminated what I think was dimly lit in my own mind and made things more clearly understood.

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