CO2 levels in 10g - The Planted Tank Forum
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post #1 of 5 (permalink) Old 08-23-2011, 09:45 PM Thread Starter
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CO2 levels in 10g

Hi all!

This is my first shot at a planted tank. I worked in a LFS for a couple of years in high school, and am just getting back into the hobby.

I am trying to figure out why my plants have not been growing very vigorously and algae (brown, green hair) has taken over on the older leaves of my plants.

10g AGA, filled to the top to minimize splashing from the filter
Aquaclear 20 HoT filter, water flow set to "low"
Fluval 20 CO2 system, one bubble per second, although this varies since the "regulator" is a joke
Liquid ferts - see below
2x 18w T5 bulbs, one roseate and one 6k (3.6wpg)
Fauna - 1 betta, 6 harlequin rasboras

Skipped most of cycling by using completely established filter media in the tank (no cloudy water or any other issues). Planted the tank about 3 weeks ago. At first the piece of driftwood I had in there was leaching a lot of tannins, and it also became covered in this goopy white blobby fungus. I cleaned the driftwood thoroughly with my hands and running water, and did a 70% water change. That really helped the light levels. I was worried about light because my glossostigma was growing up instead of out, but that didn't seem possible with 3.6WPG in a 12" tall tank... or is it? Now I wonder if the water clarity was part of the issue, with all the tannins further reducing the light penetration. But I am also just seeing slow growth and increasing amounts of algae.

At first when I tested my KH I got 3 degrees and with 1 bubble/sec of CO2 I saw the pH go down to 7 or a bit below.

I just tested my KH again and I have 6 degrees - perhaps one of the rocks in my tank is buffering the pH... sigh. But I don't mind having 6 degrees KH. However the pH is now about 7.4 and that means I have 9ppm of CO2 - too low.

The thing that has changed is that the Aquaclear filter is discharging across the length of the tank (hanging on the side instead of the back). I wonder if this is causing so much surface agitation that the CO2 can't stay dissolved?

Regarding ferts, I do Seachem trace elements 2x/week. I also have phosphate and iron supplements from Seachem. I used the K and Fe once but I saw the algae really take off afterwards so I discontinued them. I still do trace elements. But I have been scared to use the K and Fe because I know if the CO2 concentration is not right I am just going to have a ton of algae on my hands.

I would really appreciate any general tips for making sure this aquarium is on track, and in particular with the CO2 levels. I am going to get a better system than this Fluval 20, quite honestly it is junk, but I have found a cheap replacement cartridge for it so I can take my time.

In particular do you all think I am losing a lot of CO2 to surface agitation?

Thank you all, I will do my best to respond promptly. I have been lurking for a while and this is really a great forum.
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post #2 of 5 (permalink) Old 08-23-2011, 11:34 PM
Algae Grower
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As far as CO2 is concerned the easiest thing to do would be to use a drop checker with a standard 4 dkH solution like this. For the algae, while it's possible that the CO2 fluctuations are making it hard for your plants to thrive and thus easy for algae to take over it sounds like you may be lacking macros in your tank (N,P,K). Try looking around at various dosing techniques like EI or PPMD to get a feel for what nutrients need to be added to your tank. In general I think you will find that by looking at EI the assumption that excess nutrients cause algae maybe (and should) be turned on it's head.
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post #3 of 5 (permalink) Old 08-24-2011, 01:19 AM Thread Starter
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Thanks for the response. I looked at EI and PPMD and they look like they are both "mix your own" ferts methods. Right now I have the Seachem stuff (trace, potassium, iron) and I would like to use those up if possible although I certainly like the mix-your-own method for the benefits of customization and price. I've spent a lot on this tank over the past two months and want to reel it in a bit.

If I dose the Seachem ferts per their dosing instructions and do a 50% water change each week, would that be a valid method for proceeding?
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post #4 of 5 (permalink) Old 08-24-2011, 01:53 AM
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I think the take away from EI and to a lesser degree PPMD is put enough of X in the tank so that nothing is limited. Just make sure in addition to trace and K, you are adding in some N and P and more that what's needed. Different products, same result.
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post #5 of 5 (permalink) Old 08-25-2011, 01:07 AM Thread Starter
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Under what circumstances do I need to dose N? Is nitrate as measured on a test kit enough?

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algae, balance, co2, lighting

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