HOB smell


Fish Crazy
Apr 22, 2022
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Midwest US
Both of my HOBs... identical... one in a 10 gallon tank with a betta and two nerite snails and one in a 5.5 with only neo shrimp (I Know this is a betta site but it involves the betta tank) smell. For sure the biomedia (the stones in the bag on top) smell. Pretty sure the rest of the media smells too. Filters need a good clean which I'll try and do, but that's not going to fix the smell of the media, and it DOES affect my sinuses and breathing to a small degree. Is there anything that can be used to help this? The carbon needs changing in the betta's tank... and I'm actually going to put the Purigen I had was going to use for the tank I'm about to cycle in instead... I'm afraid the Purigen I just put in the shrimp tank a week or two ago is going to be smelling. THAT is easy enough to fix with some bleach, of course. But it's not doing the job I need it to in order to kill the smell in the stones and probably the sponge. The floss needs changing in the betta tank. That might help there. The floss still has 50% lifespan (at best guess, heh) in the shrimp tank. But if IT smells... short of taking out all filter media, cleaning the filters and either bleaching (?) the media or buying new... what can be done? I have one more identical filter that is clean (I had to restart my cycle... had hornwort ROT into EVERYTHING... didn't know it couldn't go in a cycling tank... and everything had to either be scrapped or soaked in bleach. (And then a hefty soak with a lot of dechlorinator of course). Vinegar didn't kill the smell at all.) So I have at least one clean filter... But is there anything else that can be added that will help reduce the smell? My basic parameters are great... 0 ammonia/nitrite... 0 nitrate in betta, just above 0 in shrimp tank... Not positive of GH and KH or pH honestly. If needed can do the tests. It's been a while. But I mean, both tanks are fully cycled and have been for about 2 years. But I have to get that smell out of the filters... and don't want to throw out all the media and risk a cycle fail... plus I'd like to use some of the betta's media to help start my ten gallon again. Please help... I also really hate using bleach because the smell gives me migraines. I can wear a mask with mint oil smothered on it when directly around it but after pouring it down the drain it lingers and spreads through my tiny apartment. Any suggestions appreciated!
Check and see if you have Cyanobacteria in the filter. It smells, and can bother people.
Cyanobacteria does smell. I have a 20 gallon with it right now. Just started 1st treatment of it using UltraLife BLUE-GREEN Slime stain remover as advised by Colin_T. Seems to be working.

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