Lights Out vs. Moonlight - Oxygen Loss? - The Planted Tank Forum
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post #1 of 5 (permalink) Old 09-14-2014, 12:44 PM Thread Starter
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Lights Out vs. Moonlight - Oxygen Loss?

I have a 90 gallon planted tank with four small discus, a couple angels, cories, clown loaches, and 16 cardinal tetras. It's about 6 weeks old, numbers all good. Plants healthy and growing, and fish are healthy. Did my weekly 50% water change yesterday and dosed with recommended amount of Excel Flourish.

I have used the moonlight setting (blue only, set at 1 out of 100) on my Ecoxotic E Series every night except two. Last night it was completely dark as I was trying to discourage some discus bullying.

Both times I set it to completely dark rather than using moonlight, in the morning all the fish were at the top of the tank gasping for air. Assuming oxygen loss, I am now blasting the water surface with the canister outflow, and they are all settling back down. I also cranked the lights to see if the plants would start breathing.

SO HERE'S MY QUESTION: Could it be just a coincidence that the two nights I went completely dark rather than using the (very dim) moonlight setting the fish were gasping for air in the morning? My only thought is that the plants might respirate CO2 far more in a completely dark environment vs. a little bit of blue light. Maybe it's the additional Excel after a water change? (Five caps rather than two).

Any thoughts?

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post #2 of 5 (permalink) Old 09-14-2014, 01:22 PM
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In my experience, they start gasping for air if your co2 is too high.

Last edited by Aceman; 09-14-2014 at 01:22 PM.
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post #3 of 5 (permalink) Old 09-14-2014, 01:32 PM
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Purely from reading not from any knowledge... my impression is very dim light doesn't have enough energy to trigger the plants to switch to photosynthesis.

When you turned the lights back on, before you started rearranging things, did they go back down or stay at the surface? Just wondering if the lighting may have triggered some other response, looking for food, etc. Are you sure it was air-gasping? My angels in certain lighting (or something -- never quite figured out what, but dim light is part of it) often go up and do that, and I know I've got plenty of oxygen, and no other fish follow.


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post #4 of 5 (permalink) Old 09-14-2014, 07:13 PM Thread Starter
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I think what helped was turning the outflow toward the surface to agitate. After about 5 minutes of that they were all back swimming around. They were definitely gasping for air. It occurred to me that when I refilled my tank yesterday I filled it fuller than usual, putting the outflow too low to create surface agitation. I'll cut the tube and raise it a bit.

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post #5 of 5 (permalink) Old 09-15-2014, 05:35 AM
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You should consider running an airstone at night to keep the water surface broken and provide some oxygen to the system.

Also, 4 discus is usually too small a number. More would cut down the bullying. I've got 6 medium-sized ones in my 65 gallon. That's pushing it, but you could definitely add more.
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