Old substrate rotting

[Kutlwano Dikgasu]

Hello everyone. I added new substate on top of my old substate about two weeks ago and the old one, that I can see, looks like it's rotting. 

The little spot in the picture looks like some mould.

What should I do?

[CJs Aquatics]

What type of substrate is that if I may ask?

[Brandon p]

I going to assume this is a sand substrate. Unless this is an organic substrate which I doubt because it’s white. If it’s way one type of substrate this is what I believe. It looks to be some sort of sand substrate. It is not rotting. What is happening is there is a lack of oxygen there. It happened in finer substrate. People often say it’s algae and most of the time it’s not but it can be a combination of the two. This is a bacteria that does not use oxygen but uses sulfIides to break down organic matter in the substrate. This is bad because The results of this is hydrogen sulfide in the aquarium. It is really easy to fix. I would remove the layer of new substrate and then remove the black or dark substrate. You can toss it or try to get the color back. The sun does do wonders. Once removed replace the substrate to prevent it watch the food or other organic materials. If you vacuum the substrate that with help mix the substrate and let the oxygen in the water get to the areas. If you want more detailed information I can provide it but this should help for now. Or I can make it simpler. This falls into my work background so I forget my audience 

[Kutlwano Dikgasu]

Thanks for the reply, the stripe of dark substate is band new Flourite, that's fine. 

I had a small layer (2cm) of pool filter sand, added a layer of Flourite and a top layer of pool filter sand.

The original layer of pool filter is what is rotting. There's a small circle on the pricture and I thing there's more I just can't see.

Thanks for the above post, I did not know of hydrogen sulfide, I'd love more information. If I have to remove the old first layer, do you think I could do it in to months?

I'll remove and save the new top layer of pool filter. Remove and save what I can of the middle, new Flourite and throw out the first old layer. 

I need two months to save for another 8kgs of Flourite. It's so expensive in South Africa.

[Brandon p]

Were these the two area’s?  
 

 

 

Edited June 19, 2022 by Brandon p

[Kutlwano Dikgasu]

Yes. There's also a lot more of that supstrate we can't see.

Ive never kept them before but would Geophagus help oxegenate the substate?

[Brandon p]

Yes, any thing that digs around. The others thing is the size of sand. The bigger the more chance it to get some oxygen. You want bacteria there it is just the bacteria that does not use oxygen that is bad. I have what is going to seem like a crazy question. Do you play golf? If you do I have an easy way to explain. I have it a pleco/ panda Cory breeding tank and don’t care much I know that there is more than enough oxygen in there I don’t worry. I a nice tank that is more of a center piece as people enter the home I just give it  a quick vacuum with the cheap gravel vacuum around the edges. Not even really to remove water even though it does I just want the sand to get mixed. It’s a 55gal and I use a vac for a 10 gallon tank. I have a video somewhere that shows this happening but I’ll have to find it. I doubt you will have any more issues with this. Sorry it’s so long. I could talk about sulfur/anaerobic eating bacteria.