The simplest and easiest thing to do and could very well be the fix. I would consider you only dropping 5 gallons of water in a 45 gallon pot the reason this is happening. Common standard is watering a pot at 1/3 or 1/4 its capacity. Which in this case, for your 45 gal pot, you should be in the 11-15gallon range...this is to fully soak your media...you probably have necrotic spots in there because you have little pockets of these 5gal daily splashes...