japeters, you're within an ace (maybe two) of being just fine. A pH of 7.3 is in the ideal range! Stop fretting.
Your phosphates may have come from buffers you have used in the past, or may have built up from the flake feed, a rich source of phosphate in the system-- or it may have come with your tapwater. Check with your water utility and see if they add polyphosphates to reduce corrosion.
Water changes will help for a start. There are resins to put in the filter to reduce PO4 (phosphate). Problem: within days they get covered with bacteria busy reducing organic phosphate to the mineralized orthophosphate algae (and plants too) can use.
There's some stuff about phosphate transformations at
www.skepticalaquarist.com A little too complicated for a post.
Your fine-haired grayish algae is often called "Black Brush Algae.' It's actually a red alga. Hell to eliminate. But that's a minor problem. Come September (they're seasonal, and you're less likely to find them sooner) you'll want to get a trio of Siamese Algae-eaters ("SAEs"), the only fish that eats red algae. (And a delightful fish in itself.)(EDIT: Oop. I just noted your RedTail Shark. He won't tolerate any other closely-related cyprinids, aka "sharks" or "shark-minnows." You have time to rethink this...)
Your problems with Clown Loaches weren't pH problems. Another bridge to cross... get that phosphate under control first, and get the plants growing strongly.
You need to get a test to measure your "KH" (alkalinity) and your GH (permanent, or general hardness).