Dear Khun Kamon
• As per you mention below tank capacity is lower than existing one. I just concerned circulation issue. Have you review or calculate about this? Please clarification.
When start washing cycle, pump consume water about 50L for stay in system (filter vessel and piping) and circulate to tank
RP Tank : capacity 300L, applicable volume = 200L so that's enough to circulate.
Washing Tank : capacity 500L, applicable volume = 325L so that's enough to circulate.
• I also recommend to have small wire way and put it over head of enclosure as below picture.