How can I improve Winkler titration accuracy for dissolved oxygen in my aquarium?

[Aria_P]

I’ve been trying to measure dissolved oxygen in my aquarium water using a homemade Winkler titration setup, but my results are inconsistent compared to my store-bought test kit. I’m following the standard method with manganese sulfate and alkaline iodide, but the endpoint color change from clear to that pale yellow is subtle and I think my starch indicator might be degrading.

[EvelynMH]

I've done a DIY Winkler setup for my aquarium too. The endpoint from clear to pale yellow always felt too subtle, and when the starch indicator sat unused for a day or two it would drift on me. I learned to keep everything cold and to prepare fresh iodide solution, but even then the readings wandered more than the store kit ever did. It felt like the indicator was the weak link.

[Mia_H]

My batch of starch went bad after a couple of weeks in the fridge. It would barely tint the solution, so the final color looked the same as the sample, which makes you miss the endpoint.

[LoganCL]

I once spent an afternoon chasing a rumor that temperature mattered more than I thought. The water in the aquarium is warm, the reagents were room temp, and I kept thinking maybe the oxygen readings were just off until I circled back to the indicator again.

[AriaH]

Do you think the real problem is the indicator degrading, or is something else in the Winkler steps dragging the numbers down?