[otomichan]

I'd love to get some help: This morning, all my desert gobies, bumblebees and lots of shrimp were at the surface. Two dead. My 29 gallon has a dense jungle of underwater plants and top entirely covered in duckweed and this has never happened before. In the afternoon, there's lots of pearling on underwater plants so I've kept the duckweed there for filtration. Could it be that there's too many plants using up oxygen during the night? Could it be too much duckweed? I added a sponge filter half and hour ago and some of the fish and shrimp are swimming around normally. What do you think?:icon_eek:

 

[jbrady33]

Are you injecting co2?

Either way it sounds like you need an airstone and/or some open water with surface agitation

 

[c_gwinner]

Your plants aren't using your O2 at night, its more than likely that there isn't any O2 left in the tank from the fish and shrimp since the surface is coated with duckweed. Need more surface agitation like jbrady has stated to allow for oxygen exchange to occur at the surface.

 

[otomichan]

Cheers. It's been a couple of hours with the sponge filter bubbling away and seeing signs of recovery. Thank goodness. So - it's good to always have some surface bare?

 

[jbrady33]

I think it is important to have someplace where liquid/gas exchange can happen - agitated and/or open surface (even if it is in the hob filter) or an airstone (Every bubble is a liquid to air exchange surface)

 

[Diana]

I would remove some duckweed. Monitor the ammonia so that if the duck weed is your major nitrogen sink you are not removing too much all at once. Perhaps clear no more than 25% of the surface at any one time. Once the other plants, growing lower, start getting more light they can probably take over some of the duckweed's job of nitrogen sink.