I'm guessing it's already gone from my water now I'm just waiting for it to process out of the fish. I was looking up half life of malachite green and formalin and I found this: "Malachite green was rapidly absorbed and concentrated in the tissues during waterborne exposure. The rate of accumulation was directly related to pH of the exposure water. After waterborne exposure, elimination of the parent compound from plasma also was triphasic with a terminal half-life of 4.7 hr."
link below
https://pubchem.ncbi.nlm.nih.gov/com...Classification
see heading 9.2 Absorption, Distribution and Excretion
and this: Formaldehyde is absorbed rapidly and almost completely from the rodent intestinal tract. In rats, about 40% of an oral dose of (14)C-formaldehyde (7 mg/kg) was eliminated as (14)C-carbon dioxide within 12 hours." 10% remains inside their body after 4 days
link below
https://pubchem.ncbi.nlm.nih.gov/compound/712
see heading 10.4 Absorption, Distribution and Excretion
So I'm guessing it should be safe to administer Metro 12-14 hours after putting the activated carbon in the sump?