How often should you change ultrasonic cleaning solution?

The signs the solution is spent

• Cleaning takes longer. The same parts need a longer cycle than they did on a fresh fill.
• Oil and sludge build up. Oil sits on the surface and sludge collects on the floor of the tank.
• The parts tell you. A dull film or flash rust after rinsing means the bath is tired or the rinse is too cool.

What wears a bath out

Three things: oil loading, suspended solids, and the chemistry being used up. Each one has its own fix.

What wears it out	What it does	The fix
Oil	Floats on top and is picked up again as the basket comes out	Skim every day, or a weir that skims it off as the tank runs
Solids	Grit and sludge settle in the tank and go back onto the parts	A filter bag or cartridge on the circulation
Chemistry used up	The bath gets weaker and cleans slower	Titrate, then top up with concentrate to the working strength

How long a bath lasts

There is no figure we can give you, and anyone who gives you one is guessing. It depends on what is coming off the parts and how much goes through the tank. Too many variables to put a week on it.

Watch the results, not the calendar. When a cycle that used to take five minutes needs ten, the bath is spent. The only way to know where a bath actually sits is to titrate it, and that takes five minutes.

How you run the tank changes it as much as what you run through it. On a bench tank the dirt settles and stays. On a floor or plant machine a pump draws the solution through bag or cartridge filters and returns it clean. Skimming, a weir and filtration all extend the bath, because they take the oil and the solids out instead of letting them build up. Why staging the clean saves chemistry.

Get the strength right, both ways

Too strong is not faster. A bath mixed over the dose attacks the parts, aluminium first, and it costs more to run.

Too weak is the one that catches people out. An alkaline cleaner attacks aluminium on its own. What stops it is the inhibitor in the concentrate, which lays a thin film on the metal. Dilute the bath and the two do not fall together — halve it and the pH moves about 0.3, so the attack barely eases, while the inhibitor falls below the level that will hold that film. An underdosed bath is close to as aggressive as a correct one and no longer protecting. Hot and weak is the worst of it.

Not every product works this way. Desludge and FX Degreaser are silicate-inhibited, and AquaVantage 1990 GD sets a hard floor of 5% when there is aluminium in the load. AquaVantage 1696 GD is near-neutral and non-silicated, so it does not apply. The data sheet for each product says which.

Check the strength, then top up

Top up with solution mixed at working strength, not water alone. Water on its own weakens the bath. Check the strength by titration once a week and top back up to the dose, instead of dumping and starting again.

For AquaVantage 815 GD the check takes five minutes with the Brulin titration kit:

1. Draw a 5 mL sample of the working bath and let it cool.
2. Add 2 drops of bromophenol blue indicator. The sample turns blue.
3. Add 1.0 N HCl titrant one drop at a time, swirling, until it turns yellow.
4. Count the drops. Drops × 0.81 = concentration %.
5. Below the target (typically 10%)? Top up with concentrate and test again.

Every product has its own factor, so read it off that product's data sheet rather than carrying this one across. Write each result down. The trend shows how fast solution is being carried out on the parts and tells you when the next top-up is due.

Some baths have their own limit. A CoreKleen HX rust and scale bath is replaced at about 15 g/L of dissolved iron. The data sheet for each product gives its dose and its limits.

Changing the solution

1. Drain the tank. Dispose of the solution as the SDS (safety data sheet) and your local trade waste rules say. Never tip it into a stormwater drain.
2. Clean the sludge off the floor of the tank and change the filter bag.
3. Fill most of the way with water, add the concentrate, then top up to the fill line.
4. Bring it to temperature and give it time to degas before you judge the clean.

The dosage calculator works out how much concentrate your tank needs.

Questions we are asked

How often should I change the solution in my ultrasonic cleaner?

When it stops cleaning in the usual time, not on a set day. If a cycle that used to take five minutes now needs ten, the solution is spent. Drain, clean the tank and refill.

How long does ultrasonic cleaning solution last?

There is no set figure. It depends on what is coming off the parts and how much goes through the tank. Watch the cycle time instead of the calendar, titrate to see where the bath sits, and skim and filter to keep it working. A trial on your parts gives your own figure.

Can a weak bath damage parts?

Yes. An alkaline cleaner is held off aluminium by the inhibitor in the concentrate. Dilute the bath and the alkalinity hardly drops while the inhibitor falls below the level that protects, so an underdosed bath is close to as aggressive as a correct one and no longer protecting. Run it at the dose on the data sheet.

Can I top up an ultrasonic cleaner with water?

No. Top up with solution mixed at working strength. Water on its own weakens the bath, it takes the inhibitor down with it, and a weak bath cleans slowly.

How do I check the strength of the solution?

By titration. For AquaVantage 815 GD it takes five minutes: a 5 mL sample, two drops of indicator, then acid titrant a drop at a time until the colour turns from blue to yellow. Drops × 0.81 = concentration %. Other products have their own factor.

What makes the solution wear out?

Three things: oil loading, suspended solids and the chemistry being used up. Skimming takes the oil, filtration takes the solids, and topping up to strength replaces the chemistry.

How do I dispose of used ultrasonic cleaning solution?

Follow the SDS (safety data sheet) for the product and your local trade waste rules. Never tip it into a stormwater drain.

Related: Cleaning solution for ultrasonic cleaners · How an industrial ultrasonic tank works · Filter bags