A mixture of coco and pebbles by Canna, available in 50 litre bags.
From The Manufacturer:
The newest addition to the Canna family, Canna Coco Pebble Mix is a mixture of 60% Canna Coco Professional Plus and 40% Canna Aqua Clay Pebbles. Coco Professional Plus is a first-rate coco product that is made using top-quality raw materials. It has the optimum structure and purity, while Canna Aqua Clay Pebbles are made from special types of clay that have a low soluble salt content.
Research carried out by Canna Research has shown that the 60/40 mix was the mixture that produced the most stable results in various tests.
Getting your plants off to a good start
A crucial factor when using an ebb and flow system is ensuring good root development in the plants. Often, only a few centimetres of feed solution is used in the pots and the excess is pumped away within ten or fifteen minutes. This is not sufficient for the food to be absorbed right up to the top of the pots. A good method to use is to fill up the containers with a mixture of coco and clay pebbles and use Canna Coco A & B. Depending on the crop's nutritional requirements, a solution of 1 ml per litre up to a maximum of 4 ml per litre will be enough. The plants can be set out immediately after the pots have been filled.
As soon as the plants have been set out, it is advisable to feed them in the regular way (i.e. from above, not from below), according to the requirements of the crop for the first week. It is crucial to only start using the (automated) ebb and flow system when the roots have reached the bottom of the pots. This will be between 6 and 10 days after the plants have been set out. As soon as the roots have reached the bottom, the standard Canna Coco feeding schedule can be used as a guide to feeding, beginning with Vegetative phase II.
Tips for watering plants from underneath
In ebb and flow systems, it is essential to ensure that the substrate remains sufficiently aereated, as many experienced growers will tell you. As soon as the roots are visible at the bottom of the pots, consider the following tips if you want to switch to watering and feeding using ebb and flow:
In the first few days, there should be enough time between waterings. This is to ensure that the medium drains sufficiently. In other words, the medium needs to dry out properly between each feed. Feeding just once or twice a week is often enough.
For crops that need more frequent feeding, it may be enough to feed them once every two days. The crucial point is that medium must not become waterlogged in order to reduce the risk of a lack of oxygen in and around the roots.
*Please note: There is a surcharge to UK customers of £6 per bag for this medium.