HYDROS pH 4.0 Calibration Fluid

HYDROS pH 4.0 Calibration Fluid is a single-use, high-precision pH 4.01 reference solution for calibrating aquarium pH probes and controllers. pH probes need two reference points to read accurately, and 4.01 is the low-end reference — used together with pH 7.0 whenever you're monitoring lower-pH water, such as a calcium reactor on a saltwater tank or most freshwater aquariums (which typically sit below 7.0 pH).

Key details

• pH value: 4.01 (low-end calibration reference)
• Best paired with: HYDROS pH 7.0 for two-point calibration of low-pH applications
• Format: high-precision single-use packet
• Shelf life: store in a cool, dry place for up to 1 year

Frequently asked questions

When should I use pH 4.0 calibration fluid? For low-pH monitoring — calcium reactors and most freshwater tanks — paired with pH 7.0.

How many calibration solutions do I need? Two, on either side of your target pH. Use 4.0 + 7.0 for low-pH water, or 7.0 + 10.0 for reef and saltwater tanks.

Which controllers use it? Any HYDROS controller with a Probe Port, such as the Control X3, X4, or Launch.

Shipped fast with expert support. Get your HYDROS gear from real reefers at Marine Concept Supply, with setup help when you need it and local pickup at our Wheeling, IL showroom.

At Marine Concept Supply, all sales are final. Due to the sensitive nature of live animals and aquatic products, we do not accept returns or exchanges under any circumstances. Please review your order carefully before completing your purchase. No Cancellations.

If you have any questions or concerns about your order, please contact us at shop@marineconceptsupply.com and we’ll do our best to assist you.

We Ship UPS and will send tracking as soon as the item ships. 

Return shipping for any approved warranties are not covered and will be subtracted from the approved credit total.

Restock Fees apply to some products, due to their size or a manufacturer policy.Each product with a restock charge is marked online, in the description.

Please inspect your order upon reception and contact us immediately if the item is defective, damaged or if you receive the wrong item, so that we can evaluate the issue and make it right