Strange organism - algae? Fungus?

Can you ID this?

This growth is slow, but it is spreading on the glass and along the stratum of my 46 gallon freshwater community tank. I have the tank planted with moderate to low light plants, also with mopani and driftwood pieces, which produce beautiful tannins in the water.

This particular organic growth is about the size of a dime in width. I cleaned two off today while doing a partial water change, which were larger and began developing centralized clusters of white eggs/spores/??? over the past few days.

I missed this smaller one, but thought to take a picture of it so I could plan my attack (with some help, of course).

Water tests at all safe and ideal levels, with very slight alkalinity.

I've obsessed with searching the web for similar images, and found one which was close, and referred to as "coralline"/"caroline" algae. However, this is a slightly salty freshwater community tank (for my Amano Shrimp).

Any ideas/advice/help would be appreciated.

 

I have never seen this. Looking at the mulm in your gravel it could be a fungus. Definitely remove it and gently vacuum your gravel.

 

Thanks! That's what we'll do then.

 

It could also be the start of a freshwater sponge. If you have salt in the water it could be a very good possibility.

 

There are a lot of freshwater varieties of sponges just as there are fresh. That looks like sponge, indeed.

 

Whats that yellow stuff?

 

There's a line of algae along/below the black (flourite?) and natural stratum ... The lighter just appears yellow through the algae with the extra light/highlights from the flash.

I was cleaning/vacuuming/water change and that area was in need, I wanted a picture first.

Are sponges good? Bad? They were attached pretty securely and rolled up like a fruit roll-up when I scraped them off.

 

This.

If in doubt, take it out.

While sponges are harmless, removing them won't hurt, either.

 

Thanks for the advice.