I currently have a 20L that has been my refugium for 20 years. A friend of mine has a drilled 40 that he gave me, and I want to replace my existing 20 with the 40. My 20 has a well established DSB, that I pretty much don’t touch. Occasionally, a small section will foul, turn black with sulfur dioxide, so I’ll reach in and stir that area with my hand to oxygenate it, but other than that, I leave it alone. So I need to transfer it to the new 40. I obviously need about double the arragonite now, and I have freshly washed available and ready to go. The question is, what do you think I should do with the old sand? I’m thinking I should rinse most of it because I’m sure at this point, it’s pretty clogged up with detritus. That may be a good or bad thing, because it is not fouled up now, and I’m sure the bacterial colony is well established. Wanting to know opinions on whether I should rinse the old gravel or just dump it in the new tank as is, gunk and all.