Newbie question

[jordsy]

My tank came with a TDS tester. It has two functions, hc and ho, but give almost the same result. What is this used for?
thx

[Matt]

The functions HO and HC are for HOLD and HOLD CANCEL. If you're taking a reading, the display will constantly sample and update. Press HO to freeze the current reading. Press HC to release it.

Simple, yes?

[Matt]

I should have been more generous in my reading. If your question was what to HC and HO do, I've answered. If you are asking what's a TDS for...

It measures the Total Dissolved Solids (impurities, effectively). It is typically used to measure the relative effectiveness of a water purification system. There are lots of posts about TDS here that a search will uncover.