Perma Salt System Manual

Perma Salt System Overview

The Perma Salt System is a salinity management approach used primarily in reef aquarium keeping and small-scale marine biology applications. It involves maintaining a stable salt concentration in a closed or semi-closed water system using automated or semi-automated dosing, evaporation compensation, and regular testing protocols. The core idea is simple: saltwater evaporates, leaving salts behind, which raises salinity over time. The Perma Salt method counters this by matching makeup water precisely to what's lost, keeping specific gravity or parts per thousand (ppt) within a tight band. You can find the official Perma Salt System Manual as a free PDF on the Perma Salt project website. It covers system design, calibration procedures, sensor maintenance, and troubleshooting. The manual is written for both DIY builders and commercial installers. I've found the 2023 revision to be the most reliable version. Earlier editions had some outdated sensor references that don't match current hardware. Here's what actually happens when you run one of these systems day to day. You have a main display tank, a refugium or sump, and a dosing pump or evaporation compensation device. A hydrometer, refractometer, or conductivity sensor reads the salinity. When evaporation exceeds a threshold, the system adds RO/DI water. When salt is drawn down or a top-off dilutes the column, it adds concentrated salt mix. The loop keeps everything sitting somewhere between 32 and 35 ppt, usually around 33.5 for most reef species.

The trick is that evaporation rates change with temperature, humidity, and flow. A fan blowing across the surface all night will move water off much faster than still air. I learned this the hard way with a tenant in my first office where the HVAC cycled differently than at home. My refractometer readings stayed steady because the float switch compensated, but the actual salinity crept up by about two full ppt over three weeks. The fix was switching from a timed top-off to a daily manual refractometer check at the same time each morning, before the chillers kicked on.

Calibration and Daily Routine

Calibrating your sensors matters more than most people admit. A $15 digital refractometer can drift half a point per month if you don't clean the prism and recalibrate against fresh water or a known standard. I use a three-point schedule: fresh RO/DI water for zero, a known salinity standard for mid-range, and a second reference point if I'm running high-precision work. Daily checks take about five minutes. Wipe the prism, take a reading, log it. If it's outside your target range, top off with RO/DI water slowly. Don't dump a gallon in at once. Shock the corals and you'll lose polyps or drive certain inverts into retreat. Add a liter over an hour through your return line, let it circulate, then check again.

Common Pitfalls and Where Beginners Go Wrong

Most new Perma Salt System users underdose their salt mix during mixing. The instructions say dissolve the powder in RODI water while stirring, but they rarely emphasize that temperature affects volume. Warm water expands. If you're mixing at 78°F and targeting 1.026 specific gravity, your actual gravity will read low until the tank cools. Wait until the water reaches operating temperature before doing a final check and adjustment. Another issue is sensor placement. If your conductivity probe sits in a dead corner where circulation is poor, it reads stale water while the rest of the tank is well-mixed. That causes overshooting. Put your sensor near a return jet or in a sump compartment with active flow. I switched mine to a drop-down tube with a powerhead pointed at it and the fluctuations dropped from ±0.5 ppt to ±0.1 ppt.

When Perma Salt Systems Fail Completely

These systems are not bulletproof. If your power goes out, you're running on batteries, or your controller dies, salinity can swing dramatically within hours depending on your evaporation rate. In summer with high fans running, I've seen a 200-gallon tank push past 36 ppt in under six hours without compensation. That kills most soft corals and stresses hard corals into bleaching. If you don't want to risk that, keep a backup manual top-off routine. Check the level gauge twice a day. Have a spray bottle of RO water ready for small corrections. And always, always keep a handheld refractometer on hand. The digital probes are convenient but they fail. I had a $300 conductivity sensor quit mid-cycle last year because the reference electrode dried out. I caught it because I was doing manual checks. Had I relied only on the automated system, I would have lost a significant portion of my tank. For larger installations or professional setups where downtime isn't an option, consider pairing the Perma Salt method with a dedicated salt dosing skimmer or a full ATC (Automatic Top-Off) controller with a separate salinity loop. They cost more and need more maintenance, but they remove the single-point-of-failure risk that bites most hobbyists.