Matsya Purana — Description of Gomedaka and Puṣkara Dvīpas; the Lokāloka Boundary; Ocean Tide...
आपूर्यमाणो ह्युदधिर् आत्मनैवाभिपूर्यते ततो वै क्षीयमाणे तु स्वात्मन्येव ह्य् अपां क्षयः //
āpūryamāṇo hyudadhir ātmanaivābhipūryate tato vai kṣīyamāṇe tu svātmanyeva hy apāṃ kṣayaḥ //
For the ocean, even while it is being filled, is truly filled by its own nature alone; and when it begins to diminish, the depletion of the waters likewise occurs within itself—by its own intrinsic cause.
It frames pralaya-like change as intrinsic and self-regulating: the cosmic waters do not depend on an external agent for increase or decrease; their filling and depletion occur “within themselves,” emphasizing an internal causal order in dissolution and re-manifestation.
By analogy, it supports the Matsya Purana’s ethic of self-discipline: stability and decline arise from one’s own conduct. A king or householder should cultivate inner restraint and right order (dharma), since prosperity and loss are portrayed as rooted in one’s own nature and actions.
No direct vastu or ritual rule is stated; however, the verse reinforces a key Vastu-Shastra principle used in Purāṇic architecture: balance and harmony are maintained by internal proportion and regulation—suggesting that sacred spaces and rites should be designed to preserve equilibrium rather than forcing excess.