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Flex-Matala sheets — the progressive filter media koi ponds are built around
Matala is a 3-D matrix of stiff curly fibers that does mechanical and biological filtration in one material. Four color-coded densities let you build a progressive stack: open Black catches the big stuff, Green and Blue trap and host bacteria, Gray polishes. Sheets are 48 × 39 × 1.5"; half and quarter sheets save you the cutting.
- Densities
- Black 190 · Green 290 · Blue 365 · Gray 460
- Full sheet
- 48 × 39 × 1.5"
- Free volume
- 92–94%
- Line
- FSM = Flex-Matala (koi)
Image coming soon
Mystic Koi’s take
Rule of thumb from Matala: one sheet of each density per 1,000 gallons in a stocked koi pond, stacked coarse to fine in the direction of flow. Holds roughly ten times its weight in sludge before you need to rinse it, and the sheets outlive most filters they go in.
What it does
- Progressive densityFour grades, one system.
- Mechanical + biologicalTraps solids and carries biofilm.
- 92–94% voidFlow stays even as it loads.
- Rinse and reuseYears of service.
- Easy to cutUtility knife or electric carving knife.
Density guide (per Matala)
| Color | Grade | Specific surface | Fiber Ø | Free volume | Role |
|---|---|---|---|---|---|
| Black | FSM190 | 190 m²/m³ (58 ft²/ft³) | 1.7 mm | 92% | First-stage mechanical |
| Green | FSM290 | 290 m²/m³ (88 ft²/ft³) | 0.9 mm | 93% | Mechanical + biological |
| Blue | FSM365 | 365 m²/m³ (111 ft²/ft³) | 0.55 mm | 94% | Fine mechanical + biological |
| Gray | FSM460 | 460 m²/m³ (140 ft²/ft³) | 0.5 mm | 94% | Polishing + biofilm |
Sheet sizes
| Size | Dimensions |
|---|---|
| Full | 48 × 39 × 1.5" |
| Half | 24 × 39 × 1.5" |
| Quarter | 24 × 19.5 × 1.5" |
Pairs well with
The science: why biological filtration matters for koi
Koi excrete ammonia through their gills, and un-ionized ammonia is toxic even at low levels, especially as pH and temperature rise. Nitrifying bacteria living on filter media convert ammonia to nitrite and then to far less harmful nitrate. The more protected surface area a filter offers — and the slower, more even the flow through it — the more bacteria it holds. Progressive-density media gives each stage its own job: coarse grades trap solids, fine grades carry the biofilm.
- Randall, D.J., Tsui, T.K.N. (2002). Ammonia toxicity in fish. Marine Pollution Bulletin 45: 17–23.
- Matala Water Technology Co. (2026). BioSteps II, EzBio and Matala filter media specifications. matala.com.tw.
Questions we get about the filter sheets
Which color do I start with?
Flow goes Black → Green → Blue → Gray. If you only buy two, make them Green and Blue.
How do I clean it?
Lift, shake and hose with pond water; a pressure washer is fine on Black and Green. Never bleach or tap-rinse the biological grades.
Matala at Mystic Koi
Matala filter media and pond equipment have been a koi-keeping staple for decades, and Mystic Koi has sold and run Matala gear in our own systems since we opened in Upland, California in 1996. Everything on this page ships from Matala USA (Sea Life Designs) or our ¾-acre facility. Not sure what fits your pond? Call or visit and we’ll size it with you.