You are effectively turning the unit every year or two, even when the tenant stays in place. 

What matters more is whether the borrower in question has the (i) time, (ii) contacts, (iii) experience, and (iv) ability to effectively communicate & package their loan request to banks & credit unions in a way that is compelling to those lenders. 

It sounds like your current property manager may not be marketing the rental effectively, and the fact that it's listed incorrectly as an apartment instead of a duplex could be turning off potential renters.

You continued to promote NB Private Capital (Brian Nelson’s firm) until the Dec 2020 when Covid hit in Q1 2020 and the effects were already known within the first month or two.

We used to hire a company to balance the chemicals and my costs were almost 2K per month.

Effectively no, otherwise everyone would do it and there would be no rent controlled buildings.If the property becomes vacant there are scenarios you can remove it from rent control. 

And it only cost them $4,000.

As a result, my bill has effectively risen from $500 bi-monthly to $700 monthly since the pipe replacement.

I know a cost segregation study would be too expensive for such a small amount of property, but is it permissible for me to estimate the value of the components on my own?

Of course, I had to make additional assumptions about the cost of property taxes, insurance etc.