Where the HydroLogic Merlin GP Carbon Filter Sits in the Line
Every Merlin-Garden Pro sends its feed water through this carbon block before the membrane sees any of it. Green coconut shell carbon fills the 17.25 in cartridge, rated at 2 GPM and good for 1,500 gallons purified. HydroLogic catalogues it as HGC728845, replacing the older HL 22080. Chlorine is the reason it exists, since it oxidizes a thin-film membrane quickly and no membrane recovers from that.
Changing the Merlin Garden Pro Green Coconut Carbon Pre-Filter on Schedule
Carbon runs out well before the sediment stage does, so most growers change it on a calendar rather than by symptom. Heavily chlorinated municipal water shortens that window; a well with no chlorine in it barely touches the carbon at all. Sequence matters here too, since sediment belongs ahead of the carbon and the membrane always sits last.
Key Features
- Green coconut shell carbon block: Coconut shell carbon holds a tighter pore structure than coal-based block, which is what handles chlorine and organic chemicals.
- Rated 2 GPM: Keeps pace with the Merlin-Garden Pro's high-flow output so the pre-filter never becomes the bottleneck.
- 1,500 gallons purified: HydroLogic's own service figure, counted as purified water rather than feed water through the housing.
- Direct HGC728845 fit: Drops into the Merlin-Garden Pro carbon housing in place of the discontinued HL 22080 cartridge.
- Membrane protection: Chlorine reaching a thin-film membrane is permanent damage, and this cartridge is the only thing standing in front of it.
Technical Specifications
| Specification | Value |
|---|---|
| Manufacturer Part | HGC728845 (replaces HL 22080) |
| Media | Green coconut shell carbon block |
| Cartridge Size | 17.25 in x 2.75 in |
| Flow Rate | 2 GPM |
| Service Life | 1,500 gallons purified |
| Reduces | Chlorine, organic chemicals, sediment |
| Compatible System | Merlin-Garden Pro |
| Weight | 1.49 lbs |