Lithium and maintenance treatment

Hello, Im 19 male of 4 yrs of remission and i wanted to ask people that were long term users of lithium about this.

I have had lithium since I was admitted for mania and it was only the combination of lithium and antipsychotics (abilify) that got me to remission...

My blood levels steadily declined as I aged and matured (being a pediatric case for bipolar) and alot of my depressive symptoms showed up on a similar time... my abilify was being tapered gradually though nothing major changed about it as I adjusted easily to each dose...

Recently I found out that my lithium level is subtherapuetic to psychiatric standards (0.53~) And my psychiatric said he just wants to bump on abilify even though my given history shows that I did better on therapeutic lithium levels, he says it "wont help with depression " and i wonder if that holds truth in psychiatric guidelines or is my psych biased against lithium...

I may just get a secound opinion but yeah...

Any insight on this?