Neither brand wins outright. Both make universal fill valves that fit most tanks, so choose by the specifics: Fluidmaster's 400H lists a 7-year warranty and a 9 to 14 inch height range, while Korky's 2X Long Life lists a 10-year warranty and 8-1/2 to 14 inches. Fit and install matter more than the logo.
How do the two brands actually compare?
Here is what each maker publishes for its flagship valve. The comparison is only as good as those listings, so check the box in your hand before you rely on any line.
| Fluidmaster 400H PerforMAX | Korky 2X Long Life (528X) | |
|---|---|---|
| Listed fit | 2 and 3 inch flush valve toilets, 1.28 to 3.5 GPF | "fits 99% of toilets" |
| Height range | 9 to 14 inches | 8-1/2 to 14 inches |
| Listed warranty | 7-year limited | 10-year |
| Water-level control | Integrated dial plus a customizable refill tube | Refill adjuster included |
| Float design | Not stated on the listing | Internal float |
| Seal material | Silicone seal, listed as chlorine and hard-water resistant | Chlorazone II rubber, listed as lasting 2 times longer than other fill valves |
Korky also sells a standard QuietFILL (528) and QuietFILL Platinum (528MP), both with a 5-year warranty. At the standard tiers the two brands look most alike.
Which one makes sense for which toilet?
A modern 1.28 GPF toilet with a weak flush or slow bowl refill. Fluidmaster pitches the 400H's "vortex refill" as raising the bowl refill rate, and it lists the 1.28 GPF floor in its fit range. Korky's Platinum model has its own refill adjuster aimed at the same job.
A tank with limited height or an odd layout. Compare the height ranges above against your tank. Korky's valve reaches a half inch shorter. Either way, you set the final height so the water-level mark sits about 1/2 inch below the top of the overflow tube (Korky's wording), and a valve set too high can run constantly or overflow.
A house with hard water. That is Phoenix. City water here tests at roughly 10 to 17.6 grains per gallon, and scale eats rubber and clogs small ports. A longer warranty and a seal material built for chlorine and minerals are reasonable tie-breakers, which is why both brands advertise them. A warranty is not a guarantee of life, though. Korky's warranty terms list "normal wear and tear" among the cases with no warranty.
A toilet you plan to keep servicing. Both brands expect you to open the valve. Korky says you can take its valve apart and service it, and sells a replacement cap assembly. Fluidmaster says to inspect the valve yearly and replace its top cap assembly (model 385) with the master seal every 5 years. Both are parts you buy for a few minutes of work.
Does the brand matter more than the install?
Not really. Most "bad fill valve" complaints are really one of four things:
- A height set too high, so water runs into the overflow tube.
- A refill tube pushed down into the overflow tube, which Korky warns can create a siphon.
- Debris in the new valve from the first time the water went back on. Kohler's troubleshooting page notes that turning the supply on and off after an install can loosen sediment in the water lines.
- Drop-in bleach or chlorine tank tablets. Fluidmaster says they damage tank components and void its warranty, and Korky's warranty lists them as an exclusion too.
Fluidmaster's fix for the debris case is to lift the cap, hold an upside-down cup over the open valve body, and turn the water on fully for three or four seconds, then off. Do that twice. Then check for leftover debris before reassembling. If you want the full setup steps, see how to adjust a Fluidmaster fill valve and how to replace a toilet flapper or fill valve.
How long should either valve last?
Korky says fill valves typically have a lifespan of 5 to 7 years, depending on the type of water you have, and notes that some water sources carry sediment that builds up inside. In a hard-water city, plan toward the short end, and treat a hissing, slow, or noisy valve as the cue to clean it or swap it. Why a toilet whistles when it fills and why a tank won't fill cover the symptoms.
When should you call a plumber instead?
Buy either brand and install it yourself if the shutoff valve turns, the supply line is sound and the tank is intact. Call a licensed plumber if the shutoff valve is stuck or leaking, the tank is cracked, the valve keeps failing within a year or two (worth a look at the water supply, since sediment is a known cause), or you would rather have the whole toilet checked in one visit. HQ Plumbing and Air handles toilet repair across the Valley, with upfront pricing before work starts.