whats this on my medium?

even better will save me a few quid. i also found on one plant i grew many moons ago, where i had gravel in the bottom.... it took up much need root space!

what many growers are unaware of is the use of sand its always good practice to add about a inch or 2 on very bottom of pot and on very top reason i say this is incase you get pests fungus gnats or anyother root eating pest cover your air vents on pot so they cannot get in or out many people will just buy there soiless mediums and just add it into pot
heres a great idea add some sand mix it throughly even little more peatmoss and of course rabbit poo or cow manure sheep manure you name it and in no time you will have a vigirious growing plant with no issues here look at my girl end of 10 th day Veg

im really interested in this mixing your own medium and seen some great results. but im a little scared as a noob, i just buy a huge ass bag and thats it. so next time i will give the sand theory a go.

also im interested in the manure thing, but horse shit is more easy to get here. will horse shit work? do i just mix in the soil and thats it for feed?