Surface Agitation

A ripple on the surface should be enough. Are you adding CO2 to the tank? How heavily planted? Do the fish gasp at the surface?

 

You could shut off the co2 at night.

 

Ok. In that case, it shouldn't be co2 poisoning in the morning which is what I was thinking. You could try running an airstone during the night and see if that changes anything. I recently added a bubble bar to my non-co2 planted 10g and both the fish and plants have drastically improved, even though I have a hob that provides surface agitation.

 

I don't run CO2 but from what I understand fluctuating levels of CO2 leads to bad algae problems.

 

If you are running pressurized, you can start the co2 an hour before lights on which should get it up within normal levels by the time the lights come on. CO2 is always offgassing all night and day anyway, you might go through a little more for the first hour each day to bring levels up but many people do this with no problem.

Fluctuating co2 levels only causes algae when the lights are on. Algae can't grow with no light. The key is to keep co2 levels stable at the same level when lights are on.

Also realize that if you start co2 for an hour before lights on, the plants won't be using any up, so levels should rise faster than if you tried to bring them up with lights on.

 

There should be no reason for Excel, I would look closer at your CO2. Get a good ripple going on top and make sure you are circulating the water in the tank. Even to the point of adding a power head for circulation. You want to see plants moving in the current during the photo period. If the tank is packed with plants, even half full, you circulation in the tank will drop off greatly. Without this the CO2 is doing what? rising to the top, where the fish hang, hence there labored breathing. I've personally done the above on several tanks. You will see more pearling and less gasping. Also, the more circulation the more CO2 and ferts can be adjusted.

Also read this, good info
http://www.barrreport.com/general-plant-topics/4324-plant-biomass-effects-over-time-current-filtration-planted-tanks.html?highlight=Flow

 

I used to notice similar gasping at the surface in the morning in my tank when using Excel. I even went to the point of staying up all night and testing O2 levels every hour over the course the evening with a LaMotte O2 kit. I found that O2 dropped from a starting level of slightly over 7 ppm (near 100% saturation at my tank temp) to close to 2.5 ppm by morning. This was not a CO2 issue at all.

My theory (and this is obviously only conjecture) is that the use of Excel can cause significant O2 depletion because it drives plant growth in a heavily planted tank to the point where, during lights-out, O2 is taken up so heavily by the plants that its concentration in the water column drops to dangerously low levels for fauna. There may also be some other oxidizing chemical reaction(s) driven by the polycycloglutaracetal in Excel that causes the depletion. In any case, as was stated earlier by Carissa, aerating the tank at night will alleviate this problem. Stopping aeration an hour or two before lights on and kicking in the CO2 supplementation should prevent any major swings in CO2 levels when photosynthesis starts.