When it goes wrong
Six things account for almost every failure in a small reservoir. For each: what you actually see, why it happens, and what to do about it — in that order, because the symptom usually points to the cause.
Almost every indoor growing problem traces back to one of four things: water temperature, dissolved oxygen, pH, or light. The six entries below are the ways those four show up on the plant.
Bolting
A central stem shooting up with a flower cluster at the top. Once it starts you cannot reverse it — but you can usually work out why it happened.
Damping off
Seedlings that come up fine and then flop over, with a pinched, water-soaked stem at soil level. It is a fungal problem and it spreads fast.
Seeds not germinating
Nothing comes up after the expected number of days. There are only five real reasons, and they are each testable.
Root rot
Roots should be white and firm. Brown, slimy or foul-smelling roots mean the root system is drowning, and the plant above will follow within days.
Algae
Green growth on the water surface, the pebbles or the inside of the bucket. Ugly, usually harmless, but it competes with the roots for oxygen.
Yellowing leaves
Yellow leaves can mean six different things. Where the yellow appears, and whether the veins stay green, narrows it down fast.
If your problem is not here, the forum is the place to ask — someone has almost certainly hit it.
Not covered here?
Post a photo and your reservoir readings. Troubleshooting threads are the most active part of the forum.
Prevention is cheaper
Most of these are avoided by holding the reservoir at 18–20 °C and changing it on schedule.
One email when there is something worth reading
New varieties, seed-saving notes, and corrections to the reference tables. No sales, no fixed schedule.