Just a quick question, where did u purchase the pump from? The seller cant help u? You should really buy from some1 who is professional and could give u good advise. For example, if ur plumber has done the piping as per ur photo, you will have some problems after the installation....

a) The most important thing, you need to install PVC unions as per grundfos requirements.

b) If cold water is boosted by the water pump while the hot water is using water tank's water, your hot water pressure will b much weaker than the cold water. So, when u r showering, you will feel the water is not hot enough as u r getting more cold water than hot. Therefore, the tank's outlet should go into your pump then split to ur heater and down to your bathroom. By doing this, you will have same pressure for both hot and cold.

c) The pump by pass is wrong. Imagine u r using 8-10" rain shower but ur pump is out of order, so you will b using the pump by pass. However, the water supply is from the tank, do you think u will have sufficient water pressure to power up the rain showers? You should do a main water by pass instead.

Here is how the installation should look like


Hope that answers ur question