The first PPFD survey of the planted layout, since superseded by the 8 August re-run.
How is usable light actually distributed across a 90P under a single pendant fixture?
The tank is 90 cm long and lit by one pendant fixture that is considerably narrower. Plant placement had been decided by eye. Before spending anything on a different light, it was worth establishing what the current one actually delivers at each plant.
Light would fall off toward the ends, but the working assumption was that the fixture was simply underpowered for the tank.
Recorded before measuring, so it can be shown to have been wrong.
An Apogee MQ-510 underwater quantum sensor was held level at each numbered plant position, mid-photoperiod, with the aquarium light on and room lighting minimized. It was run twice: seventeen positions on the 1st of August and all twenty on the 2nd.
The standing survey demonstrates highly uneven PPFD distribution across this 90P. It does not yet establish that the lower outer readings are biologically limiting. Center readings sat inside the working range used for demanding red plants, while the end positions read a fraction of that; measured against the range for what is actually planted at those ends, which is deliberately tolerant, no position reads below its range.
A figure describing a fixture over open water does not describe what plants at the ends of a planted layout receive. The original premise, that the fixture was too weak, was not supported by the readings. The original Solar RGB still produces strong center output after roughly six years of use, while PPFD varies substantially across the tank. Mounting height was the first no-cost adjustment tested. Per-position measurement is now the basis for evaluating the layout.
Results describe this specific aquarium under the conditions recorded above. They are observations, not universal recommendations.