How many days is the cobra? Circular containers huh? Have you considered transplanting your cobra into a much larger square container? The reason i ask is that when roots extend laterally from the tap root they make contact with the side of the container and in the case of circular pots this causes the root to grow round the inside of the container, winding round the existing root mass whilst adhering to the side of the container. This can lead to root mass strangulation and a loss of surface area efficiency in the root system. When square containers are used the lateral roots make contact with the side of the container and are diverted back into the growing media at an angle <90 degrees. This leads to an abundant network of roots in the growing medium, where the nodules are growing back and fourth across the soil and prevents strangulation. Soil pH fluctuations due to the uneven distribution of salt build ups and root rot are common pathologies of root strangulation. This is similar to the symptoms pot-boundness where the root mass exceeds the volume of the container and strangulation arises. Square containers are usually available in most hydroponic or specialist horticultural stores (which i prefer).
