GroStar GS4 5-in-1 Combo Pen

One Pen for pH, EC, PPM, and Temperature

Carrying a separate pH pen and a separate EC pen means two devices to calibrate, store, and remember to bring on a walkthrough, when a single feed-solution check usually calls for both readings anyway. The GroStar GS4 combines pH, EC, dual PPM scales, and temperature into one 5-in-1 pen, cutting a two-device routine down to one.

It uses the same replaceable double-junction probe design as GroStar's dedicated pens, so a worn probe swaps out on its own, and the pen ships with a full calibration kit to get every measurement dialed in from the start.

Key Features & Benefits

• 5-in-1 measurement — reads pH, EC, PPM (500 scale), PPM (700 scale), and temperature from one pen.
• Replaceable double-junction probe — swaps in a new probe without replacing the whole meter body when accuracy drifts.
• 3-color backlit display — shows each reading clearly at a glance, even in low grow-room light.
• IP67 waterproof housing — holds up to splashes and brief submersion during reservoir testing.
• Ships with a full calibration kit — includes what's needed to calibrate every measurement type without a separate solutions purchase.

Who Should Use the GS4

Growers who want pH, EC, and PPM covered by a single pen instead of carrying separate dedicated meters are the fit for the GS4, particularly anyone doing frequent reservoir or runoff checks where switching devices slows the routine.

About GroStar

The GS4 is part of the GroStar meter line manufactured by Apera Instruments, a water-quality and horticultural testing equipment maker, and is backed by the same two-year instrument and one-year probe warranty as the rest of the GroStar lineup.

Frequently Asked Questions

How do I calibrate all five measurements on the GS4?

Use the included full calibration kit and the pen's built-in calibration function, typically calibrating pH and EC separately against their own reference solutions; temperature and the PPM scales are derived from those two calibrated readings. Recalibrate on a regular schedule to keep every measurement accurate.

When would I choose the GS4 over a single-purpose GS1 or GS3?

Choose the GS4 when a single check needs both pH and EC data, since carrying one combo pen instead of two dedicated pens saves time on a routine walkthrough. A dedicated single-purpose pen can still make sense for a grower who only ever checks one parameter.

Is the GS4's probe compatible with other GroStar pens?

The GS4 uses the same replaceable double-junction probe design as GroStar's other pH-capable pens, and it's built to fit all GroStar replacement probes, simplifying which spare parts to keep on hand. That shared design also means one spare probe can potentially serve more than one pen model.

Is the GS4 waterproof enough for regular field use?

Yes, its IP67 housing is rated for splashes and brief submersion, which covers typical reservoir and runoff testing conditions in a working grow space. Dry it off after use even so, since prolonged submersion beyond the IP67 rating isn't recommended.

What's included when I buy the GS4?

It ships with a full calibration kit covering pH and EC calibration, so every measurement type is ready to dial in without a separate solutions purchase. That's a meaningful savings over sourcing pH and EC calibration solutions separately.