Formula one is excellent as well and soaking in real garlic shouldn’t affect your no3 problems. Usually overfeeding is the main problem along with overstocking. You’re a little overstocked for a 20 SW tank so keeping up with pwc is critical to keep your levels straight. I also think somewhere in your tank excess detritus is building up creating your no3 problem. Just doing 10+% pwc each week should have your no3 pretty close to 0 so I’d try vacuuming the sand bed again to remove the detritus that gets buried in it. You don’t need to go deep, usually just the first 1” is where most of it collects and if using a large enough siphon you should not disturb it too much.
Also have you tested the distilled water for no3? The quality of distilled water found in grocery stores can vary so I’d make sure the no3 is 0 and if it does have any switch brands.
Also have you tested the distilled water for no3? The quality of distilled water found in grocery stores can vary so I’d make sure the no3 is 0 and if it does have any switch brands.
