As far as marker, this stuff marks well, and a little goes quite far. My suggestion to the company would be a better storage container. This will leak and get everywhere. I placed bottle in a zip lock freezer bag, and a lot of dye found its way out of the bottle some how. I would suggest a leak proof top with a smaller pouring hole. I poured all the dye into a large Dawn dish soap bottle and it worked great. No leaks and was much easier to control the pour.

Works wonderfully and 1 oz is more than enough for 1 gallon of spray. Only downside is it VERY messy to pour (keep inside a storage bag if possible to catch inevitable leaks). Best bet would be to get a syringe (~30ml is an ounce) and draw directly from the container. On the upside, it does wash off concrete with water. If you have a garden hose it's nothing to wash off when your done. If you opt to pour directly from the container, as others have said, wear old clothes and shoes you don't mind getting dye all over and expect your hands and arms to look like a smurf. I subtracted 1 star simply due to container design. If it had a spout, or even a lip, to rest when pouring, easily 5 stars all around.

This is not as concentrated as other dyes I have used. I should not have purchased it because this value is not indicated on the packaging. Most will show the concentration as a percentage of Acid Blue #9. The reason I give this product 3 stars is for the lousy lid that comes on the jug. It has a "child safety" push-to-turn lid that WILL NOT close tightly. Once I moved the contents from this jug into another one with a better lid I quit making a mess. I won't buy it again.

This stuff definitely marks the spray. I had a different brand last time I sprayed and you could hardly see it. This stuff is the opposite, it works very well. I mixed it a little on the "strong" side at first, but reduced it on the next batches. The only problem I had with it was that it is very messy. You just touch this stuff and it will want to get on everything. It does come off fairly easily. Rinses off plastic, will stain wood mulch, stains skin, but comes off with soap and scrubbing - and time.

for whatever reason, when I used the blue marker in the spring with the hand held bottle sprayer (high volume), the marker didn't work well (it wasn't visible enough), even though the concentration should have been more than adequate. But I just tried it with my backpack sprayer, at less than 1 ounce per gallon of water, and the results were excellent.