Anoxic Gravel

[SynoSteff]

Hi there,

I have a fishtank with Synodontis nigriventris (zebra variety).
The gravel below where I feed them is going anoxic. When i disturb it bubble come up and the gravel at the bottom is turning black (it was originally white) it also just smells anoxic.

The tank is part of a system with 6 tanks in total. 1 tank is a filter, with carbon, zeolite and filter sponge and the others all have syno's in. Only the nigriventris tank has the major anoxic problem. I think it may be cause the fish crowd in a single hiding place so I think all the waste is concentrated in one area. They are also not very good eaters so there is sometimes left over food. I think it's this combo that is causing the anoxic bottom gravel. I have recently added a compressor with a large airstone in each tank to try and increase the oxygen concentration in the system but this hasn't helped :(
Could it be that my gravel layer is too thick and there is not enough water movement down there? It's about 4-5cm thick.

Would setting up an undergravel filter on that side of the tank maybe help? At least maybe get some water circulating down there?

Any response would be greatly appreciated.

Thanks :)

[SynoSteff]

Seesh this forum is active. How are you supposed to get your post seen? hehe

[rrkss]

If the gravel is anoxic, I would reccomend that you take the fish out before you try to do any major work to fix the problem. Anoxic gravel can produce toxic sulfur based compound that could kill your fish otherwise. 4-5 cm of gravel quite a lot. In my fish only tanks, I keep 1 cm to 1 1/2 cm at most. Take the fish out of the tank and store them in a plastic bucket with the filter attached to the bucket. Then you want to drain the water out of the tank and thoroughly clean the gravel/decoration even taking the gravel out and washing it with tap water to clean up the anoxic areas. Anoxic gravel is not very healthy in a freshwater system and provides more risks than rewards. Consider reducing the gravelbed to 1 - 1 1/2 cm to prevent this from occuring again.

[IceH2O]

I don't know much about anoxic gravel.But it sounds like you need something to help mix up the gravel.You don't have that deep of a bed to be causing it.

Maybe you should add some MTS,they hide in the gravel during the day,moving thru it and this itself would help the circulation.At night they'll eat any algae in the tanks.

Another option if you don't feel like messing with snails would be some of the loaches.Kuhlis and a few others like to burrow into the sand,they would help stir it up some.

If you just don't feel like adding any of the above a good rule of thumb is when you do a water change just take the end of a net,or a stick and run it thru the sand.That way it never has a chance to build up.

[IceH2O]

4-5 cm of gravel quite a lot.

Thats only like 2 inches of gravel.I'd hardly call that a lot.

[SynoSteff]

Thanks guys. I dont think it primarily because the gravel is thick. I think it's because i have lots of fish and they hide in the same small spot at a high density and therefore there is a high deposition of waste material in one area. Thus causing anoxic conditions. It is only in this area where the gravel is anoxic.

I will clean the tank tomorrow. I will remove lots of the gravel just in case. As well as put in an under gravel filter that covers the area. Hope this helps. If you have any other suggestions please let me know :) thanks

[IceH2O]

If its gravel and only in that certain spot why not just do a gravel cleaning? That would suck up all the bad stuff and wouldn't release it into the water.

How often do you do WCs and gravel cleanings?

What are your water parameters?

[Roan Art]

If its gravel and only in that certain spot why not just do a gravel cleaning? That would suck up all the bad stuff and wouldn't release it into the water.Was just going to ask the same thing. Sounds like all he really needs is a gravel vac.

Roan

[SynoSteff]

I've been doing quite a bit of gravel cleaning lately but it isn't really helping too much the area is quite badly effected. With 6 tanks (1.2m) it also becomes quite a hassel ;) so I think i'm going to try the thinner gravel layer. The tanks are only there to hold my broodstock so the aesthetics aren't key. I just hate glass floors and I dont think cats like them too much either. Want to keep them as happy as possible.

Will check my water in the morning and post a reply when I get home later

Do u think th UG filter will help with water flow through the gravel or am I wasting my time?

Thanks so much for your help :)

[SynoSteff]

I did a good gravel vac this morning but there will be new gas under there tomorrow and the gravel is pretty nasty down there. Will try do it more often and more consistently. How often is a good gravel vac in order? hehe

Also pretty keen on the UG plates if they'll help ;)

[rrkss]

A reverse flow undergravel filter might do the trick. 2 inches of gravel is a lot in my opinion. To much gravel for dirt to get trapped in and will eventually become anoxic. 1/2 an inch of gravel looks nice also but won't have this problem.

[TKOS]

If they are unplanted tanks and you just want a gravel layer for look s then I would say yes, just remove as much gravel as possible. A UGF would help but since it requires a tank tear down at this point just going with a thin layer of gravel seems easiest.

[SynoSteff]

What's a reverse flow under gravel filter? It won't be too hard to put in an under gravel filter. I only want to put it on 1 side so I'll take the fish out, take all the gravel on 1 side out, put in the UG plate and then just smooth the left over gravel over.

Thanks so much for the input guys, I really appreciate it :)

[Soulcoffr]

Reverse flow undergravel filter (RUGF) is where instead of pulling water up the UGF tubes with an airstone or a power head, you reverse the flow down the tube with a powerhead that's designed for reverse flow.

Like this one... (It's model 660R)
http://www.drsfostersmith.com/Product/Prod_Display.cfm?pcatid=4628&N=2004+113040

The advantage of RUGF is that you're pushing the fresh water under the plate, and therefore the gravel is oxygenated from the bottom up. So there's far less chance of anoxic pockets and there's also less crud that builds up under the UG plates because the water is prefiltered at the powerhead.