Sulfur smell in tank with sand substrate

[cideon]

So I've got a 65 gal tank which was going to be a growout for my poor Jack Dempsey and Severum, but when I moved to an apt more than a year ago, (and just this fall to a house), I have not been able to bring that and another tank to permit them more room. But I have been changing their water weekly or at least twice a month at my mom's for over a year (and the tank was set up about 1-2 years before that). Granted, some weeks it's 90% if I didn't get to do it the preceding week, and when I do keep on track, I only do 50%-ish. They've been doing OK healthwise, but today's WC brought up a big problem. I had never thought much about stirring the sand substrate, thinking the layer was too small to breed a colony of anaerobic bacteria, but I found out I was wrong. I didn't have the lights on, and was really only paying attention to the water level when I filled it up, but I noticed I'd made a huge mess of cloudy water and I did get the smell of sulfur that is different than the one I get at the beginning of filling when I add my prime. So from what I understand, i need to stir the substrate and do some more water changes. But how to go about it?

I have no temporary tank to move my fish to, so they will have to stay in there no matter what I do. Is it best to just mess up all the sand at once and do another 90-95% change? Or would that be too much of another shock, and should I only do like a quarter of the sand and 90% WC? And then repeat as son as I can? (I want to do SOMETHING today, but I'm going out of town for a few days tomorrow, so I want to make sure they'll be OK without me being able to do an emergency change tomorrow, ya know?)

EDIT: Forgot to mention I can't check my parameters if you all need those because I have left my testers packed in some box somewhere for now :<

 

[duanes]

Does sound like hydrogen sulfide pockets.
Vacuuming the sand when doing a water changes usually prevents this.
And/or keeping MTS snails, helps prevent the sand to compacting, and they also constantly breakdown the debris that can rot and turn to the H2S.

 

[skjl47]

Hello; During a series of water changes the sand can be siphoned out with the water thru a hose. If you do not have rooted plants( probably not with a jack dempsy and a severum) the tank can be emptied of sand after a few water changes.

If you do not wish to have the tank in various stages of less and less sand, then a clean amount of sand can be kept to replaced that siphoned during a single water change. Might take a while longer this way.

I agree with the MTS (snails) and have them in most tanks.

 

[cideon]

I was thinking of getting some for this tank later and a future tank to prevent the problem. But what should I do today? Little sand movement or all of it? I would think what wasn't disturbed earlier is safe not being moved (so just do a little tonight and each weekly WC), but I'm not sure if maybe it's leaching small bits of the toxic gases if I leave it be?

 

[duanes]

When vacuuming you don't need to remove the sand, the H2S will bubble up the vacuum tube as you disturb it.
When I vacuum, the sand gets sucked maybe 1/3 or half way up the tube, then falls back by gravity while smaller, lighter organic particles are removed with the old water.