Mold or algae?

[Coinee]

I have had a tank sitting idle with water and cycling for the past while. It cycled a while ago, however I haven't added anything in it at all, I've just been slowly feeding it ammonia for the past month and doing water changes. The sand came from my already established jar but the rock in the tank was completely new dry rock. 

 

I was just going to start transferring everything over to this tank when I noticed some dark purple-ish colouring in the silicone on the back edges. Is this algae or mold? Some of it had grown above the water line but some of it was below the waterline. I think it has been there for a little while but I'm not sure since I haven't looked at the tank too closely until now. 

 

When I tried to clean it with a tissue, it rubs off as purple and I can't seem to remove it all since it's under the silicone. Technically since it is under the silicone, the means water can get under there. Would it be safer to just toss the tank (It's new and I've never used it before and its held water all along for the past two months) ? 

 

My gut tells me this is algae since I've never seen mold this colour before but I'd rather be safe than sorry.

 

[Jacob319]

I’m almost positive it’s beneficial bacteria 

[Coinee]

1 hour ago, Jacob319 said:

I’m almost positive it’s beneficial bacteria 

Seems a little strange to me because it's only on the silicone, not on the rocks or anywhere else in the tank. 

[Christopher Marks]

Hmm, that does seem unusual. Is it possible the transferred live sand could have introduced coralline algae? Under the silicone seems really strange though, I don't think coralline would grow there.

[Coinee]

7 minutes ago, Christopher Marks said:

Hmm, that does seem unusual. Is it possible the transferred live sand could have introduced coralline algae? Under the silicone seems really strange though, I don't think coralline would grow there.

It's certainly possible. I do have a bit of coralline algae in my jar on some rocks.

 

I looked on google and it seems some people do have coralline algae growing under their silicone. But I'm a bit skeptical, I don't want to have a mold habitat and kill my corals haha.

[Jacob319]

I’m almost positive it’s beneficial bacteria

3 hours ago, Coinee said:

Seems a little strange to me because it's only on the silicone, not on the rocks or anywhere else in the tank. 

Well what I’ve got on my liverock looks almost exactly like that but on a larger scale cause it covers every inch of it cause I was scared at first as well but when I researched and looked into other well established tanks it’s everywhere so I wouldn’t recommend getting rid of it

[Coinee]

1 hour ago, Jacob319 said:

I’m almost positive it’s beneficial bacteria

Well what I’ve got on my liverock looks almost exactly like that but on a larger scale cause it covers every inch of it cause I was scared at first as well but when I researched and looked into other well established tanks it’s everywhere so I wouldn’t recommend getting rid of it

Are you thinking more so of "coralline algae" or diatoms and not beneficial bacteria? Because beneficial bacteria shouldn't be visible like this. Live rock that is purple-ish and covered with this colour is usually due to coralline algae.  I am believing it to be coralline but I'd like some most opinions before I risk a some corals.

[Jacob319]

11 hours ago, Coinee said:

Are you thinking more so of "coralline algae" or diatoms and not beneficial bacteria? Because beneficial bacteria shouldn't be visible like this. Live rock that is purple-ish and covered with this colour is usually due to coralline algae.  I am believing it to be coralline but I'd like some most opinions before I risk a some corals.

Yeah I meant coraline algae my mind was a tad scrambled when I wrote it in here sorry about that

[Coinee]

So, I took the entire aquarium apart and looked around inside. There is more purple stuff on the bottom silicone. That bottom part was always submersed in water, so it's probably not mold. Additionally, when I wiped it away, it was purpleish-pinkish which seems consistent with coralline. There seems to be more where the sand is (which was sand directly from my jar) so it makes sense that there would be more coralline around the live part. 

 

So, I'm gonna say "Solved". Thanks guys.

[Jacob319]

Yes glad to know it’s not mold