Seachem Purigen & Macro Algae

[chromakey]

Hi:

I just did all my test with API test kit:

s.g.: 1.025
PH: 8.2
Ca: 420
Nitrite, nitrate, ammonia: 0
kH: 8
PO4: 0

I don't usually dose with any additives. I just do water changes every two weeks. I do have some older additives around so I added a bit for Ca & hardness buffer.

In my other tank the "grape" macro algae turned white and went mushy. I removed it all. I am not sure what causes this.

Thanks,
Michael