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"Reading" Red Root Floaters

March 15, 2023 2 min read

Phyllanthus fluitans red root floaters

Nitrate levels matter.

Excess contributes to algae problems. Sustained deficiency stunts plant growth and makes them vulnerable over time.

To measure nitrate levels, one can use a test kit. Experienced aquarists can also judge from plant coloration and form.

While it takes some practice to ‘read' submerged plants, the common red root floater (Phyllanthus fluitans) above turns out to be a surprisingly easy-to-use indicator.

Red root floaters

Above: At sustained very low nitrate levels, they turn deep red.

Red root floaters

Above: At high nitrate levels, they turn completely green.

The red floaters were grown at around 200 umols of PAR compared to the green floaters at 400+ umols of PAR. Stronger light can turn them redder, but the relative impact of nitrate levels is greater.

How to use them:

  • If you wonder about the broad level of nitrates in your aquarium and don’t want to use a test kit, red root floaters is a fun way to get an indication. Remember: the clue is in the colour of the NEW leaves that develop in the tank.
  • If your red root floaters are very green and if you are struggling with algae problems, especially Green Dust Algae, lowering nitrates is one factor that often helps. Use APT 1 which has no nitrates, or reduce dosage of APT 3.
  • If your red root floaters are extremely red for a long time, it may indicate overly lean conditions. Plants may look healthy, but can be very fragile. This is common in very mature tanks that use lean dosing.

How to read the signals

  • Observe only the newest leaves. Like ’tree rings’, the older leaves record the past, the newest leaves the most recent environment.
  • Other things being constant, if the new leaves are turning redder, your nitrate levels are dropping.
  • Other things being constant, If the new leaves are turning greener, your nitrate levels are rising.

Target colour?

In most 2Hr Tanks, residual nitrate (NO3) levels in the water generally measure below 5ppm (more often, close to zero) at the end of a regular week before water change. This is the residual reading after plant absorption, and at these levels, plants are healthy and it is easy to keep algae under control.

At <5ppm, red root floaters are greenish-yellow-red as shown below. However they are more useful as directional indicators, and not to gauge the absolute amount of nitrates present.

Phyllanthus fluitans red root floater