Fluidized sand bed issues

[mano]

First off I have over 5 years of aquaculture experience and am currently breeding seahorses in a system with a 100 gal sump, about 900 gal of tanks, a 70 gal bead filter, and about a 300 gal fluidized sand bed (only about half full of sand though). Today I backwashed my bead filter which I do about every two weeks and this causes the fluidized bed filter to get stirred a little too. Today when I did it though I got a whiff of hydrogen sulfide and the water in the fluidized bed filter was slightly greyish/black in color. I've never seen this before and I can't figure out what happened since I did everything how I normally do? The only thing I can think of is that the probes going down into the filter to keep it fluidized somehow got plugged and then caused some dead spots. Does anyone have an experience with these or have any idea what happened? I didn't not design this particular system and have been told that it could have been designed better but it has been working fine in the past when I backwashed the bead filter.

Any ideas or advice would be appreciated. Thanks!

Christine

[dga]

its very possible there are dead spots. is the unit clear to be able to watch the backwashing process? i used to have a small 1 gallon capacity vertical fluidized filter that was clear, and after a few months general skum would build up in some areas causing it to be stagnet. with my small filter i could just shake it to dislodge the sand, after which would spit out considerable amount of junk and a failt smell of hydrogen sulfide.

[mano]

Thanks for the response dga. No the unit isn't clear, it's about 7 feet tall and made out of fiberglass I believe. I wonder if there is some way I can stir it up better...maybe stick a clean broom down in there to mix it up a bit more?

[dga]

if there is access from the top, a clean long handled stick or broom handle could do the trick. im not sure on the exact type of filter your using but i have read some are somewhat pressurized so caution should be used when removing ports or access plates.

[mano]

The top is open so I should be able to try the broom stick thing. Thanks!