Need a little insight on algae

[Kfactor]

Hi all I’ve had this brown like algae on my back wall of my main tank and not it’s in my frag tank I just hooked up to my sump . I have about 2 ppm of no3 and 0 po4 so I just started dosing brightwell po4 on Friday and still zero My total water volume is around 40g . I started with 1 ml the first day / second day i did another 1ml still nothing / third day I did 2 ml still nothing / today I dosed 3 and see if that brings it up . What do you guys think would be causing this algae

 

[Kfactor]

Bump

 

[Crustaceon]

Essentially, that algae is going to absorb the P04 as fast as you add it, hence the zero P04 reading. I used to dose phosphates too and gave up on it because I felt like I was chasing a number and freaking out because my hanna checker was saying zero all while my sps looked perfectly fine. I feel like it’s better sometimes to go by what the tank is telling you than what test kit shows on a color chart. I have the same annoying brown mystery algae on my back panel and started running phosguard even with the hanna zero reading. That algae is starting to clear up and I’m getting better colors out of my acros. Apparently there’s just plenty of P04 in my system but it’s just locked up in algae and is gradually being re-released as it wastes away.