Is this algae harmful

I know I have diatom algae on sand bed but this is blackish... it reminds me of mold but not real fuzzy..I've got a little bit out & it all stays together when I use my little rake to pick it up.. in picture it is the stuff by the elegance..
In this pic you can see a little of the black on top of the brown diatom.
Thanks for any help..

 

That looks like cyanobacteria and it can smother your corals if allowed to get out of control. Keep removing it as it occurs. Make sure you have low nitrates and phosphates.

 

First pic looks like red slime. What are your parameters currently at? That's something you will want to find the root cause of in order to deal with it.

 

it looks like cyano to be too. As 2 in 10 said, you'll want to manually remove it, you should be able to ciphon it off pretty easily is what people say

is your tank still pretty new? Diatoms usually show up first after a newly established tank cycles and then the other uglies show up. You will want to check your parameters to see if things are ok, if newly cycled then that's the reason for the algae so just remove it. Altho I should say, even if newly cycled, you'll want to know your parameters

 

Parameters are as follow...
Sg=1.026
Nitrates=.50ppm
Phosphate = 0.04ppm
Ammonia = 0
Nitrites=0
PH=8.3
Alk=3.0meq/8.4dkh
Mg= over 1600ppm.. had probs lately with this staying real high..
Cal= 440
Hope I didn't miss anything..

 

Numbers look good except Mag. You want to get it down to around 1300. Check whatever you are dosing and see if it adds Mag. Disconinue it and get something that does not add Mag.

 

Looks like red slime to me also. The Cyano I dealt with was more stringy, it grows like strains of hair.

 

Yea I know mg is to high... I haven't been dosing lately... I've got my tank on the red sea reef program & only dose according to parameters...I test for coral colors 2-3 times a week, algae weekly, & foundation parameters weekly.. I only use red sea coral pro salt & it does have mg & last water change was about 2 1/2 weeks ago... its been doing great & I think all that came in on a couple new frags I got in...

 

Personally I would work on getting the phos and nitrate values down.

Many ways to do that.

 

According to red sea reef program nitrates & phosphates are decent for accelerated coral growth or coral colors... needs these algae nutrients for the zooxanthellae...here are 2 pics of what red sea reef program recommends for accelerated growth & coloration...
I usually don't let them even get this high.. I dose the red sea no pox..good stuff!