It’s hard to have a 3W handheld laser built for $150. I built a laser. I used a laser diode from a DLP projector, flashlight, and some 18650 batteries. It also required some custom circuits I won’t disclose for safety measures. It’s not a toy. I’m not sure of the laser power output. I’m sure it’s north of 2W. A laser that pops a balloon or burns a paper towel is around 150mW. Mine will set the grass on fire, light fireworks, ignite gunpowder (all of these from 10 feet away). I have laser goggles and it’s still absurdly bright. It runs for about 40 seconds before the batteries are dead.

Think about the physics involved to “burn” pests off a rock in an aquarium. How thick is the glass? How much water is in the tank? How far is the rock from the glass? Saltwater or fresh water? All these things effect the beam at the point of impact. There’s more physics going on here than there is for a 2500 yard rifle shot! Light dispersion through water and the thermodynamics of the energy transfer through said water are some hairy math which I don’t care to ever do again. Also, the minerals in said water will have an effect on the beam, so the wavelength of the light becomes a factor.

Additionally, to measure your laser’s output power, you need a very costly laser output power meter, or you’ll have to design a precision experiment.

All this said, my guess, to burn said pests in say a 100 gallon fresh water tank, where the rock is approx 8” from the 1/4” glass, you would need to focus the beam to less than 1mm, and have a 800nm laser power of >7W. Since that’s an IR beam, you’d want an aiming laser as well (5mW red). A 7W laser needs a huge cooling system as well as a massive current source. Remember, lease diodes are sluts for current. They’ll draw as much as they can until they burn out. The must have some kind of current limiter.

Get a refund if you can and clean your tank the old fashioned away. I know it sucks and you’re afraid of disturbing an ecosystem, but unless I see someone do it in person, I have to believe it can’t be done.

I remember in college we used to go to the observatory near Mooreland, OK and use those green laser pointers all night long! Now, I’d think it’s a bad idea with all the crap of people pointing lasers at planes. That was almost 15 years ago and that 5mW green laser pointer was probably $300 at the time. Now they’re less than $30!

The first laser I ever had/bought/acquired came from the surplus sale at the University of Oklahoma around 2001 or 2002. I was 19 or 20. It was a 2.5W HeNe laser made around 1988. It was probably 12 feet long. I had a long bed truck and it hung off the bed with the tailgate down. It needed multiple voltages from a power supply, but I think the big end was 18VDC @ 200A! Remember, lasers are sluts for current! Anyways, it ended up having a cracked cooling tube and I sold it for parts on eBay but what I’m getting at is how much laser technology has changed in 30 years. I have a similar output device that is now handheld and operates off the same batteries as most people’s vape mods

Don’t take the batteries fresh off charge and put them in and use it. You can damage the diode.

That $30 amazon laser is probably suffice...

I don’t know about your laser, but on mine, I needed a regulated voltage multiplier. Some of these handheld lasers that use those 18650 batteries don’t have a regulator. I’m sure some have a multiplier as well. Charge your batteries and immediately take them off and measure them with your DMM on VDC. That 3.6VDC battery fresh off charge can be as high as 6VDC. Batteries in series means 12VDC through an unregulated multiplier could be issues...

That’s probably a 5W diode but a 1W supply. I don’t know how you could ever have big enough batteries in that size to supply enough current for the diode. OP, if you have one, get a benchtop power supply, set the potential limit to 6VDC and the current limit to 5A and see if it’s brighter than with the batteries. I haven’t tried it (mostly because I loaned out my Lambda power supply and haven’t got it back) but I’m certain my laser is way under performing with batteries. I’ve considered building a bigger battery tube and running it 12 18650s rather than 2 but I really need to do some math and make sure I’m not going to cook the diode. I doubt I have enough heat sink.