The short answer: For most glasses, plain lukewarm water is enough in an ultrasonic cleaner, and adding a single drop of mild dish soap helps with oily lenses. Purpose-made cleaning tablets or concentrates work well too. What you should never pour in is alcohol, acetone, ammonia glass cleaner or other solvents, because they can damage lens coatings and aren't safe in an ultrasonic tank.
Why the solution matters less than you'd think
An ultrasonic cleaner does the real work with cavitation: sound waves create tiny bubbles that scrub every surface of your glasses. The liquid in the tank is mostly there to carry those waves. That's why plain water already does a good job. The solution you add only needs to help break down oil and skin grease so the bubbles can lift it away.
Plain water: the safe default
Lukewarm or room-temperature tap water is the simplest, safest choice for everyday cleaning. It's coating-safe, costs nothing, and rinses clean. For glasses that are just dusty or lightly smudged, water on its own in a 3-minute cycle is usually all you need. If you live in a hard-water area, you may see faint mineral spots after drying, which a quick microfiber pat removes.
Water plus a drop of dish soap
When lenses are greasy from skin oil, sunscreen or makeup, add one small drop of plain dish soap to the water. Dish soap is a mild surfactant that loosens oil without harsh chemistry. Keep it to a single drop, since too much creates foam that dampens the ultrasonic action. Rinse well afterward so no residue dries on the lens.
Cleaning tablets and concentrates
Purpose-made ultrasonic tablets or eyewear-safe concentrates are formulated to clean without attacking coatings. They're convenient and consistent, and a good option if you clean jewelry or other small items in the same unit. The main downside is cost over time compared with water and dish soap. Always check that the product is labelled safe for coated lenses before using it on AR or blue-light glasses.
What to never put in
- Rubbing alcohol or isopropyl. Can degrade AR and other coatings over repeated use, and is flammable.
- Acetone or nail polish remover. Aggressive solvent that damages both coatings and many frame plastics.
- Ammonia-based glass cleaner (e.g. Windex). Formulated for windows, not coated eyewear.
- Bleach or strong household cleaners. Corrosive and unsafe in an ultrasonic tank.
- Undiluted essential oils or vinegar in large amounts. Vinegar is acidic; skip it for coated lenses.
A simple routine that works
- Fill the tank with lukewarm water to the line.
- For oily lenses, add one drop of mild dish soap (or an eyewear-safe tablet).
- Submerge the glasses fully and run a 3-minute cycle.
- Rinse under clean water.
- Pat dry with a clean microfiber cloth.
If you want a cleaner sized for eyewear and tested as coating-safe, Lensio runs this routine in about three minutes.
The honest trade-off
No solution will remove scratches or restore a worn coating, and even the best one can't beat physics: very heavy grime may need a second cycle. Tablets add cost, while water and dish soap are nearly free but slightly less convenient. For the vast majority of people, water with the occasional drop of soap is the best balance of safe, cheap and effective.
Frequently asked questions
Can I use just tap water?
Yes. Plain lukewarm tap water is coating-safe and works well for everyday cleaning. Add a drop of dish soap only when lenses are oily.
Is dish soap safe for my coated lenses?
A single drop of mild dish soap diluted in water is fine and rinses away cleanly. Avoid soaps with heavy fragrances, moisturizers or abrasives.
Do I need special ultrasonic tablets?
No, they're optional. They're convenient and consistent, but water with dish soap cleans glasses well at a much lower cost.