- Sku: 80305
- Vendor: Fritz
Fritz RPM Liquid PT 2 Calcium | 2-Part Calcium Supplement for Reef Aquariums
Fritz RPM Liquid PT 2 Calcium is part two of the Fritz Reef Pro Mineral two-part dosing system, formulated to replenish the calcium (Ca) consumed by SPS, LPS, and soft corals as they build their carbonate skeletons. Pharmaceutical-grade and made in the USA, RPM PT 2 keeps your reef chemistry rock-solid between water changes.
Pair PT 2 with Fritz RPM PT 1 (Alkalinity) for full two-part dosing, and verify levels with a precision Salifert Calcium Test Kit or Hanna Marine Calcium Checker HC. Browse the full additives & supplements collection for the rest of your reef chemistry lineup.
How It Works
Corals consume calcium and alkalinity in roughly equal proportion as they grow their calcium-carbonate skeletons. As Ca drops, coral growth stalls and skeletons can stop forming. RPM PT 2 delivers a balanced liquid calcium supplement that you dose daily — alongside RPM PT 1 (alkalinity) — to keep calcium steady in the reef-safe range of 400–450 ppm.
Features — All Sizes
Choose Your Size — Variant Comparison
Select a size in the tab section below for the full individual spec sheet.
| Spec | 16 oz | 32 oz | 1 Gallon | 5 Gallon |
|---|---|---|---|---|
| Volume | 473 mL | 946 mL | 3.78 L | 18.9 L |
| SKU | 80305 | 80306 | 80308 | 80309 |
| Form Factor | Round bottle | Round bottle | Jug w/ handle | Bucket w/ handle |
| Ideal For | Nano / pico reefs | Small reefs 20–60 gal | Mid reefs 60–180 gal | Large / multi-tank systems |
| Works With Dosers | ✓ | ✓ | ✓ | ✓ |
Detailed Variant Specifications
Click a size below to view its full specification sheet.
16 oz · Nano-Reef Bottle · SKU 80305
The 16 oz bottle is sized for nano and pico reef hobbyists running tanks up to about 20 gallons, or for anyone trialling RPM dosing before committing to a larger jug.
| Specification | Value |
|---|---|
| SKU | 80305 |
| Volume | 16 fl oz (473 mL) |
| Best for | Nano & pico reefs (≤ 20 gal) |
| Dispensing | Pour cap, manual or doser |
| Brand | Fritz Aquatics |
| Made In | USA |
32 oz · Small-Reef Bottle · SKU 80306
The 32 oz bottle is the everyday size for small reefs in the 20–60 gallon range. About double the dosing runway of the 16 oz with the same convenient bottle format.
| Specification | Value |
|---|---|
| SKU | 80306 |
| Volume | 32 fl oz (946 mL) |
| Best for | Small reefs (20–60 gal) |
| Dispensing | Pour cap, manual or doser |
| Brand | Fritz Aquatics |
| Made In | USA |
1 Gallon · Mid-Reef Jug · SKU 80308
The 1 Gallon jug is the sweet spot for the typical mid-sized reef tank (60–180 gallons). Best value per ounce for hobbyists running daily two-part doses with a peristaltic doser.
| Specification | Value |
|---|---|
| SKU | 80308 |
| Volume | 1 US Gallon (3.78 L) |
| Best for | Mid reefs (60–180 gal) |
| Dispensing | Carry handle, gravity-feed or doser pickup |
| Brand | Fritz Aquatics |
| Made In | USA |
5 Gallon · Large-System Bucket · SKU 80309
The 5 Gallon bucket is built for large reefs, frag systems, and multi-tank fishrooms. Months of dosing runway in one container; pulls comfortably with a stiff dosing tube and weighted strainer.
| Specification | Value |
|---|---|
| SKU | 80309 |
| Volume | 5 US Gallons (18.9 L) |
| Best for | Large reefs, frag tanks, multi-tank rooms |
| Dispensing | Sealed bucket w/ handle, dosing tube pickup |
| Brand | Fritz Aquatics |
| Made In | USA |
Which Size Is Right for You?
16 oz — Pick this for pico/nano reefs (≤ 20 gal), or to trial RPM dosing before stepping up.
32 oz — The everyday size for small reefs in the 20–60 gallon range.
1 Gallon — Best value for the typical mid-reef hobbyist running daily two-part doses on a 60–180 gallon system.
5 Gallon — The choice for large reefs, frag systems, and anyone running multiple tanks who wants months of runway.
How to Dose
Test your current calcium to establish a baseline. As a starting point, dose 1 mL of RPM PT 2 per gallon of tank water to raise calcium approximately 2.5 ppm — then adjust based on your daily consumption rate after running a 48-hour test sequence. Always dose PT 1 and PT 2 separately (different times of day, or different points in the sump) to avoid precipitation. Never combine them in the same dosing reservoir.
FAQ
Do I need to dose PT 1 (Alkalinity) at the same time?
Yes — RPM is a two-part system. Calcium and alkalinity are consumed together by coral skeletal growth, so dose roughly equal volumes of PT 1 and PT 2 daily, spaced apart by at least an hour to prevent precipitation.
What calcium level should I target?
Most reef hobbyists target 400–450 ppm calcium. SPS-dominant tanks often run on the higher end and prioritize stability over absolute number.
Will PT 2 affect pH or alkalinity?
PT 2 is calcium chloride based and is pH-neutral. It does not directly affect alkalinity, which is why PT 1 must be dosed alongside.
Can I use this in a fish-only saltwater tank?
You can, but there's no need — fish-only systems don't consume calcium quickly. Weekly water changes with a quality reef salt cover everything a FOWLR tank needs.
Is it safe for refugiums, sumps, and inverts?
Yes. RPM PT 2 is reef-safe when dosed at the recommended rate and is compatible with shrimp, snails, starfish, anemones, and macroalgae refugiums.
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Fritz RPM Liquid PT 2 Calcium | 2-Part Calcium Supplement for Reef Aquariums
