There were some studies a while back that show that the waterborne bacteria get most of the NH4 and within minutes. This is why organic carbon dosing raises these populations faster making them able to skimmed and removed - they have the first shot at any carbon source and also the fuel. It is just a proximity thing. You can study this with a really good ORP and oxygen probe and watch the oxygen levels decrease a little bit during feedings when the fish tend to excrete to make room for the new food - the oxygen levels drop as the bacteria get fuel and reproduce. Then, the corals will be happy to consume some ammonia too.
I don't know that I have ever seen a study that explicitly shows what parts of ammonia get to the corals or algae.
If anybody remembers back in the olden days - for me the 1990s in the US - we used to test ammonia all the time. I always wanted to see a tinge of yellow, but not too much. This eventually went away when people could not understand "throughput" and wanted to see a concrete residual number on a test kit... so the end result of nitrate was the thing that people tested for and worried about since it was more "concrete."
This is kinda off topic, but my answer to lots of algae issues are urchins, like Lasse likes to post about. They are voracious eaters, will eat macro, hair, anything and will even eat coralline once the soft algae is gone. I loaned 3 to a friend with bryopsis and they crushed it in about a month. I think that a lot of people dismiss them because they do eat coralline, but trust me when I tell you that everybody who is good at this hobby comes to hate coralline too. I get Pincushions from the Florida Keys from Reeftopia - they are white and pink, look good, hardy and long lived. They cannot really live in tanks with high poison (N and P) concentrations, but if you have lower levels, they will do quite well. My only irritation is that they sometimes pick up ill-mounted frags and carry them around the tank as decorations and protection. Unlike snails, they can live off of coralline and don't die off when the algae is all gone.
I do vacuum my sand starting in about year four and do about 1/4 of the sand every quarter. I do not believe that detritus is bad and totally believe that it is mostly benign, but I do think that it "gums up" the works not allowing the water to permeate to the lower depths and not allowing the conchs and cucumbers access to the whole depth. I also want the water to permeate so that there are not pockets and areas where the sand will have more phosphate bound than other places - this is where most of the phosphate release comes from.
We do see a lot. For sure. Most of these are proximity issues... GHA on the rocks where the rocks are releasing terrestrial po4 still. I am going to argue until the day that I die that any tank with NSW level of N and P levels that has algae has consumer issues, not building block issues.
