Ideal environmental conditions for coral growth encompass warm, clear, shallow water that receives abundant sunlight and maintains a stable salt concentration.

Coral reefs flourish in tropical, shallow waters, typically ranging from $20^\circ C$ to $28^\circ C$. This temperature range is a key reason why they are predominantly located in the region between the Tropics of Cancer and Capricorn. The warm water is vital for the survival of tiny, colorful organisms known as polyps, which constitute the structure of coral reefs. These polyps engage in a symbiotic relationship with a type of algae called zooxanthellae, which require sunlight for photosynthesis to produce food. Consequently, clear water is essential as it allows sunlight to penetrate effectively.

The depth of the water also plays a critical role in coral growth. Coral reefs generally thrive in depths of less than $50$ meters to ensure that the zooxanthellae receive sufficient sunlight. Nevertheless, some coral species can endure depths of up to $300$ meters.

Moreover, coral reefs necessitate a stable salt concentration, as fluctuations in salinity can induce stress in corals, potentially leading to bleaching. The optimal salinity range for coral growth is approximately $34$ to $37$ parts per thousand.

Additionally, coral reefs prefer environments with moderate wave action. Waves are vital for distributing nutrients and oxygen, both of which are essential for coral health. However, excessive wave strength or strong currents can inflict damage on the delicate structures of coral.

Lastly, corals require a solid substrate for attachment. They cannot thrive on sandy or muddy bottoms, as these materials are too unstable. Instead, corals favor rocky outcrops or the skeletons of deceased corals for anchorage.

In conclusion, the ideal conditions for coral growth involve a delicate interplay of several factors, including temperature, light, depth, salinity, wave action, and substrate. Alterations in any of these variables can significantly affect the health and survival of coral reefs.