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Re: Rotten Substrate/gravel vacuuming

I have a 55 gallon tank, not fully planted. I vacuum religiously when 
changing water. I figure if it's sitting on top of the substrate, it's not 
fertilizing, it's polluting. I also have a tendency to feed well.

I've been dealing with part of the tank going anaerobic for a while. While 
observing the tank, I noticed that a bubble would emerge now and then and go 
to the surface. While vacuuming, I plunged the cleaner through the substrate 
to the glass bottom, and tons of bubbles appeared (in the vacuum). The water 
was disgustingly smelly. I rooted around a bit and discovered other areas 
were also smelly, though the gaseous bubbles were in one area particularly.

I pondered what to do. It's a low light tank, and quick-rooting plants didn't 
seem to be an option (as they wouldn't grow). One thought was to put heating 
pads on the bottom to increase circulation. I ran an air wand on that side of 
the tank at night for a while to create a water current (though a very 
low-power air pump). Checking from time to time, I noticed that it did help 
diminish the area, but there were still rotten spots, and gas.  I'd actually 
go in and dig with my hands and feel the gas pressure. I finally got a power 
head for that side of the tank. I toyed with the idea of connecting a hose on 
the output and sticking it directly in the gravel (isn't that what they make 
undergravel filters for?), but decided to just try running it as is, to see 
if the current alone would solve the problem. After a cleaning today, the 
smell and gas appear to be entirely gone.


<< >Does anyone have any input into my earlier question about whether to 
 >vac planted tank substrate?  I have an area of the tank that gets dirty and 
 >when gravel vacuumed pulls up some nasty smelling stuff.  Should I leave it 
 >in there for the plants?  All advice appreciated.
 I wouldn't leave it.
 Not good. H2S is a bad sign(rotten egg smell ?). Black color is very bad
 too. Vac the effected area well. Add fast growing rooty plants to see how
 they do. Watch closely for signs of poor growth. Consider adding larger or
 more porous gravel topped with regular sand that your using.
 The area is going anaerobic and need something to get more O2 down there.
 Roots from faster growing plants might be a way. Adding small pieces of lava
 or SeaChem's Matrix to the mix will help or some Turface etc will help too.
 Adding a small airline tube with some water flow through it will solve this
 too if you place it down into the effected area. This can help a trouble
 spot but I think the plants or/and the gravel changing will help the most
 for the long term. Also consider lowering the depth of gravel in this area
 or adjusting the flow so water current goes into to it more.
 Mulm is great for tanks but black stinky stuff is bad. I leave the mulm but
 would take care of the black nasty stuff fast. Check archives for more info.