help! lotus declining
After almost 3 months of tripling in size w/ new leaves almost every day, my lotus began declining a few weeks ago! Can anyone tell lotus newbie what to do?
Details: bought 3-gal dwarf lotus pot from a reputable nursery, added 3 lotus fertilizer stakes around rim (as specified by manufacturer for that size container) then placed it 4"-5" under water on submerged base in 2' x 2.5' metal barrel pot w/ bubbler filter. Given that pot's location btwn 2 bldgs only has sun approx 10:30/11:00 to about 1/2:00, I purchased lotus cultivar that does well w/ half day of bright shade. Fairly constant marine layer here @ beach (sunset zone 22); temperatures range from generally mid-70s (day) to mid-60s (night), although few days in mid-80s around July 4th. windy sometimes...very happy, beautiful plant w/ stunning growth for about 6-8 weeks.
Then, about 3-4 weeks ago, found some dark aphid-like bugs on leaves & tried to remove them by hand before infestation grew. Two days later, found scale as well on some leaves and many stems. Did hand removal again. Infestation increased. So, since there were abundant leaves without pests, went for nuclear option & cut off all infested leaves + stems @ water line (about 10-15% of leaves).
About 7-10 days later, noticed lotus decline: No new leaves for 14 days & existing leaves die from center out (see photos). Also lost all my duckweed or azolla.
About 5 days ago basically changed all water... 4 small new leaves came up w/in couple days. No big new big leaves...no more small leaves since.
What can I do? Pls help.
BTW, Water here is very high in phosphates.