I used to use Seachem Excel and when it ran out, I filled half of the 500 mL bottle with DI
water and the other half with Glutaraldehyde. That resulted in a solution similar to Excel. Plus, the bottle protected the glut from light (which will break it down). I would then dose 1 mL to every 2 gallons daily. If you are just starting out, I would go with a lower dosage and gradually increase it. Be careful; some plants do not tolerate it well (anacharis and Vals).
I use a pediatric oral medicine syringe (grocery store, $0.79) attached to a shot length of air line tubing. I shoot it into the current produced by the HOB
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