That blue/grey vessel right in front of the heater is a Nature2 chlorine puck and mineral system. Mineral systems are not recommended by this site. Pucks are also not recommended due to each puck adding CYA to your water. Eventually your CYA gets so high that your pool is unmanageable. The same company (Nature2 - a Zodiac/Jandy company) make the exact same vessel in a saltwater chlorine generator (SWG). So you could convert your pool to a saltwater pool, which creates its own chlorine, and no longer have to manually add chlorine. Just a thought.
If you are going to end up cutting everything anyway to get to the heater, there are other, better alternatives to the Nature2 SWG, however.
Can you post a wider shot of the entire equipment pad?
Nature2 Fusion soft system is an all-in-one salt water swimming pool sanitizer and mineral system for in-ground pools.
www.nature2.com