Strong smell

[RandomTeaPig]

Could it be hydrogen sulfide smell. Maybe the gravel has caused some water to become stagnent and moving the gravel has released the gas.
Also it could be rotting fish flakes that have splashed onto the aquarium lid. Maybe look and clean the aquarium lid if you see any rotting fish flakes.

It definately not an eggy smell as such. Neither of my tanks have lids but will check the braces as you never know. I started my big tank cleans and found and removed a few dead snails that dont smell too great but different kind of smell.
Had my windows open most of yesterday and today and you cant really smell anything in the house now. Only really smell it if your above the tanks themselves which i can live with.

[LookoutTrout]

Was it a smell like petrichor? That's the smell released by dried earth when it rains. I'm not that wordy, just saw it somewhere else and it fairly well describes the smell of my tank.
https://en.m.wikipedia.org/wiki/Petrichor