UltraSonic Waterproof Sensor

Perhaps someone can help me, with a weird issue I am having.

I have a Waterproof ultrasonic Reader https://www.dfrobot.com/product-1503.html version2 , I connected it to a Wemos D1 R2 Built in Wifi Board that is based on the Arduino Chipset , I also have a Relay connected to that Board. https://www.robotics.org.za/REL4-OPTO?search=relay


This is a Very Basic setup.

Measure the Water volume in the Tank then switch on the pump and updates this with wifi to my server.

Here is the Question.

I connected a 9v power supply AC to DC to the Arduino Board and the Arduino Board then Gives power to the Relay and Ultrasonic Meter.

I then Measure the Water level and the Water Level is not accurate at all it shoot between 40% full to 70% full this is after I did readings of 10 times and took the avrg.

But when I take a normal 9v Block Battery the Measuring is - very accurate and it stays Perfect
I thought it is the Power Supply so I replaced the power supply - No Luck Same Issue
I then used my Laptop to Drive the Arduino Board and again it is - very accurate and it stays Perfect
I then Replaced the Arduino Board - No Luck Same Issue
I then tried to build a 5V Capacitor with a 7805 Regulator Chip to make the 5V as smooth as I can - No Luck Same Issue

I also read that the Version2 Water proof Ultra sonic read can do this
https://www.youtube.com/watch?v=N42Y-QOqwtA


What else can I try

Just an idea Please will help

Thanks