Avoid spraying the solution on metal or electrical , it is a corrosive .

Basically the corrosion restricts the flow of water overtime giving you very little water pressure.

This is likely caused by corrosion. 

The rental is pretty old and the plumbing in the basement is starting to show blue corrosion on the pipes and I am concerned this will lead to bigger issues in the future.I don't feel comfortable taking on this as a DIY as I believe there will need to be soldering done to remove/replace some sections.

I'm curious, though, if that would be corrosive to the various pipe materials (cast iron, clay, orangeburg)This could be more drastic but not as expensive, but can you simply cut the trees down near your line?  

Old metal lines are usually so packed with corrosion that your water barley flows.I probably would not purchase as a rental but definatly as a flip assuming price adjustment to reflect costs.

Corrosion will happen regardless of whether it's gas or electric, so it's worth doing it for both.Also, my understanding is that since the gas heater's burners are at the bottom, the sediment can act as an insulator, reducing efficiency (although there are varying opinions on this.)Prior to flushing the tank, you should test the TPR valve.

Regarding the screen, recommend any types that are corrosion resistant? 

But chlorine is a corrosive chemical, and some of the components on the roof may not like it so much (Rubber gaskets, galvanized nails)Detergents also act as surfactants.

Bleach is also corrosive and contains dioxins.In your country the OSHA and EPA no longer endorse the use of bleach for mould remediation.Hydrogen peroxide is not the be-all-end-all mould treatment, it is one of the more effective products available to those of us who are not professional remediation services.