Algae outbreaks look causeless when light, feeding and fertiliser changes live in your memory, because algae answers a change a week or more later and memory credits whatever you did last. Keep one combined log where every weekly entry carries exactly eight fields: date; light period; intensity setting; change made; glass score; rockwork score; plant-leaf score; and feeding or fertiliser change. Eight fields, in that order, every week — the pairing of dated light settings with dated surface scores is what turns guesswork into cause and effect.
Score Three Surfaces, the Same Way Weekly
Score each named surface from 0 for clean to 3 for heavily coated, at the same point in your weekly routine, before any cleaning disturbs the evidence. Glass shows green dust and spots first; rockwork grows the tougher films and tufts; plant leaves reveal whether algae is outpacing plant growth, which points toward light or fertiliser rather than feeding alone. A worked entry, using only the eight fields: “Date: 3 March. Light period: eight hours. Intensity setting: unchanged at the middle setting. Change made: none. Glass score: 1. Rockwork score: 1. Plant-leaf score: 2. Feeding or fertiliser change: fertiliser dose held steady.” Three separate scores matter because surfaces disagree, and the surface that worsens first often names the driver before the others react.
Log the Light Settings You Actually Ran
Record the light period the timer actually delivered and the intensity setting in use, not the settings you intended. Timers slip after power cuts, dimmers get knocked during cleaning, and a log of intentions conceals both accidents. Enter every change in the change-made field on the day you make it, including moving the light unit, replacing a tube or unit, and adding or removing floating plants that shade the water. Note also any week when strong daylight reached the tank through a window, recorded inside the change-made field, because sunlight is a light change even though no setting moved.
Change One Variable, Then Wait
Use the log to discipline your response: when scores climb, change the light settings or the feeding or fertiliser — one side only — and hold everything else steady for at least two weekly entries. Algae's delayed response means a change judged after three days gets credited or blamed wrongly; the dated entries let the scores from two weeks after a change speak for that change. Enter feeding and fertiliser adjustments in the final field even when the light stays untouched, because excess nutrients feed algae as surely as excess light, and an unrecorded fertiliser increase will otherwise masquerade as a lighting problem in your data.
Read Three Outbreaks Back Together
After several entries, read the log as a story: find each rise in scores, then look at the entries one to two weeks before the rise and identify what changed there. A period extension, a fertiliser increase, a missed water-change week — the culprit usually sits in that window, named by your own records. Write the finding at the foot of the log and the response you chose, so the next outbreak starts from knowledge rather than folklore. Kept continuously, the combined record also protects a settled tank: when scores sit at 0 or 1 for months, the entries prove which light period and feeding level your tank thrives under, and any helper can reproduce those settings exactly. Filed with the tank's maintenance history, that proof stays available, and KinsLe's Pet Passport holds the whole combined record in one packet, ready when the next green film appears.