Hi gooner,chinaryukin

A typical siphon and 10m hose will be used to change the water. May left a bit old water and should not be any problem. Correct me if i were wrong.
There will be sunlight shining on the pond through the window from 8am to 12am. May give a try first. If the result is not good, may move the pond to outside. Hopes this answer your question.
Chinaryukin, your ranchus are very nice. Keep up the good job. I will collect mine this weekend. May need your care-taking help.
Thank you.