In car wash chemistry, two chelating agents dominate new formulations: GLDA (glutamic acid N,N-diacetic acid) and MGDA (methylglycine-N,N-diacetic acid). Both replaced the phased-out EDTA and NTA, both are classified as ‘readily biodegradable’ per OECD 301B, both have REACH green-lights. But choosing between them is a concrete technical decision based on water hardness, formulation pH, wash type and ESG strategy. This guide gives a decision matrix without evasive “it depends”.
TL;DR:
- MGDA wins for hard water (>250 mg CaCO₃/L), touchless alkaline washes (pH >11), closed-loop installations, when iron (Fe³⁺) and copper chelation strength matters.
- GLDA wins for soft/medium water (<250 mg CaCO₃/L), formulations at pH 4–11 (detailing, hand wash), when budget is tight, when the customer buys on “bio-based origin”.
- For most central/northern European regions (water 200–400 mg/L hardness) — MGDA is the safer pick.
Chelation strength — the key fact
The stability constant (log K) is the hard comparative parameter:
| Ion | log K_GLDA | log K_MGDA | Conclusion |
|---|---|---|---|
| Ca²⁺ | 5.2 | 7.0 | MGDA binds Ca two orders of magnitude stronger |
| Mg²⁺ | 5.2 | 6.8 | MGDA stronger |
| Fe³⁺ | 11.7 | 16.5 | MGDA much stronger — critical for rust from coolers |
| Cu²⁺ | 13.0 | 13.8 | Comparable, MGDA marginally better |
| Zn²⁺ | 9.8 | 10.9 | MGDA better |
Practical meaning: for typical EU hard water (300 mg CaCO₃/L ≈ 3 mM Ca²⁺), MGDA requires ~0.3% in working solution, GLDA ~0.5% for the same binding effect. That’s an economic difference: MGDA’s lower dose offsets its higher unit cost.
pH activity range
GLDA and MGDA differ in chelate stability as a function of pH:
| pH range | GLDA | MGDA |
|---|---|---|
| 2–4 (acidic) | Weakly active | Active |
| 4–7 (slightly acidic/neutral) | Optimal | Active |
| 7–10 (alkaline) | Optimal | Optimal |
| 10–12 (strongly alkaline) | Active | Optimal |
| 12–14 (extremely alkaline) | Weak | Active |
Consequence: for acid wash (wheel cleaner, limescale removal) — MGDA. For touchless alkaline formulations (concentrate pH 12–14) — MGDA. For neutral/slightly alkaline foam (hand wash, detailing) — GLDA suffices and is cheaper.
OECD 301B biodegradability (28 days)
Measurement of DOC (dissolved organic carbon) reduction in 28 days:
| Chelator | OECD 301B (28d) | Classification |
|---|---|---|
| EDTA | 3–9% | Persistent (phased out) |
| NTA | 60% | Inherently biodegradable |
| GLDA | 60–80% | Readily biodegradable |
| MGDA | 75–90% | Readily biodegradable |
MGDA degrades faster and more completely — critical for municipal treatment plants and closed-loop installations (accumulation after many wash water recirculation cycles). GLDA also qualifies as ‘readily’ but slower kinetics mean higher effluent concentrations across days of wash traffic fluctuation.
EU Ecolabel status: both accepted for detergents (Decision 2017/1217). Both compliant with EU Detergents Regulation 648/2004.
Cost per litre of working solution
Raw cost per kg isn’t enough — what matters is cost per litre of effectively chelated water. Assumption: chemistry must chelate 300 mg CaCO₃/L (EU hard water), dilution 1:100.
| Parameter | GLDA | MGDA |
|---|---|---|
| Wholesale price (EUR/kg, 2026) | 3.9 | 4.7 |
| Concentration in concentrate | 8% | 5% |
| Chelator cost in 1 L concentrate | 0.31 EUR | 0.24 EUR |
| Chelator cost in 100 L working solution (1:100) | 0.0031 EUR | 0.0024 EUR |
MGDA wins on cost by ~22% for hard water, thanks to lower required concentration. For medium-hardness water (150 mg CaCO₃/L), MGDA and GLDA come out comparable. For soft water (<100 mg CaCO₃/L), GLDA wins, because higher concentration doesn’t hurt (ion isn’t the limit) and lower unit price decides.
Accumulation in closed-loop systems
Car washes with closed-loop water recycling reuse 80–90% of water. Chelators accumulate over successive cycles until their biodegradation in the settling tank matches new input. Here MGDA wins clearly:
- GLDA: after 5 recirculation cycles, chelator concentration rises to ~3× nominal (slow degradation kinetics)
- MGDA: after 5 cycles, concentration ~1.5× nominal (fast tank degradation)
High GLDA accumulation causes: (1) “chelation leakage” into recycled water, (2) higher risk of disrupting oil separator performance, (3) increased OBT (Organic Bound Tracer) in sewer effluent. For closed-loop car washes MGDA is practically the standard.
Decision matrix — your car wash
| Context | Water hardness | Formula pH | Wash type | Recommendation |
|---|---|---|---|---|
| Urban touchless (EU avg) | 200–400 mg/L | 12–14 | Touchless | MGDA (PRO) |
| Rural touchless (very hard water) | 400–600 mg/L | 12–14 | Touchless | MGDA + booster |
| Professional hand wash | 150–300 mg/L | 8–10 | Manual | GLDA (ECO) |
| Premium detailing | any | 7–9 | Hand wash | GLDA (bio-narrative) |
| Closed-loop network | any | any | Touchless/Manual | MGDA (accumulation) |
| Acid wheel cleaning | any | 2–4 | Spot wash | MGDA (pH range) |
| Eco-certified detailing | any | 8–10 | Manual | GLDA (bio-based) |
| Small wash, soft water | <150 mg/L | 8–11 | Manual/Touchless | GLDA (price) |
What Fortis Foam uses
Fortis Foam PRO (concentrate pH 13.8, touchless) — MGDA as primary chelator (5% in concentrate). Stability at extreme alkaline pH + high chelation kinetics for Ca/Mg/Fe are required for high-throughput touchless car washes with often hard regional water.
Fortis Foam ECO (pH 10.5, hand wash/detailing) — GLDA as primary chelator (8% in concentrate). Lower formula pH sits in GLDA’s optimal range, bio-based origin fits premium detailing narrative, lower unit price offsets the higher concentration needed for the same effect.
For operators with very hard water (>400 mg CaCO₃/L) or calcium-scale buildup issues on wash bay equipment, we offer MGDA boosters on request — contact us for specifications.
Summary
- MGDA stronger, wider pH range, better biodegradation, more expensive per kg, wins on cost for hard water and extreme pH.
- GLDA bio-based, cheaper per kg, wins for soft/medium water, neutral pH, premium narrative.
- For most central/northern EU regions (water 200–400 mg CaCO₃/L) — MGDA.
- In closed-loop systems — MGDA due to lower accumulation.
- Full comparison including EDTA and NTA: EDTA vs GLDA vs MGDA. Theoretical background of chelation: chelating agents in car shampoo — hard water guide.