Why Is My Fibre Slow? How to Fix Slow WiFi at Home

If you're paying for 100 Mbps but a speed test shows 30, take a breath before you phone your ISP to complain. In the large majority of cases the fibre line is delivering exactly what you pay for - and the speed is being lost inside your home, over WiFi.

A speed test run over WiFi almost always understates your line, because WiFi sheds speed through walls, distance and interference, and an old or ISP-supplied router can cap throughput well below the line rate. The fastest way to prove it: plug a laptop straight into the fibre box with a network cable. If you get full speed wired but not wireless, the fix is in your hands - and this guide walks you through it.

Start by establishing the facts with a proper speed test, then work through the checks below.

Before changing anything, isolate the problem with one decisive test, recommended by South African ISPs like Afrihost:

1. Connect a laptop directly to the fibre box (ONT) or router with an Ethernet cable.
2. Disconnect or switch off WiFi on that laptop, and make it the only active device.
3. Run a speed test against a local (Cape Town or Johannesburg) server, several times.

If the wired result is at or near your package speed (allow about ±10%), your fibre is fine and the problem is your WiFi or devices - keep reading. If the wired result is also far below your package, that points to a line-side issue worth raising with your ISP.

WiFi is convenient, but it's a shared radio signal that degrades with distance and obstacles. A few specifics explain most slow-WiFi complaints:

• 2.4 GHz vs 5 GHz: the older 2.4 GHz band realistically tops out around 50-100 Mbps and is crowded - it overlaps with neighbours, microwaves, Bluetooth and cordless phones. The 5 GHz band is far faster but doesn't travel through walls as well. Use 5 GHz near the router for speed, and 2.4 GHz for range and smart-home devices in far rooms.
• WiFi 6 and 6E: newer standards carry far more data and handle busy homes better. A modern WiFi 6 router reaches link rates well above 1 Gbps, and WiFi 6E adds a clean 6 GHz band with no neighbour congestion.
• Channel congestion: in flats and estates, dozens of routers fight over the same channels. Setting a clear 5 GHz channel can lift speeds noticeably.
• Placement and range: distance and obstacles are the biggest real-world killers. A router stuffed in a cupboard or behind a TV against a brick wall will never perform.

The single most common hardware culprit in South African homes is the router itself - often the free unit supplied at installation. Watch for:

• 100 Mbps Ethernet ports: a classic trap. If the router's LAN ports are 100 Mbps (not gigabit), even a wired test caps at about 90 Mbps no matter how fast your line. A green LAN light usually means a gigabit link; orange often means a 100 Mbps link.
• Single-band or old-standard routers: 2.4 GHz-only or WiFi 4/5 units simply can't deliver modern fibre speeds over the air.
• Coverage limits: one router can't blanket a large or double-storey home. A mesh WiFi system fixes dead zones far better than a single unit and usually removes the 100 Mbps-port problem at the same time.

Sometimes the slow device is the one running the test. Older phones and laptops have older WiFi chips (WiFi 4/5, single antenna) that cap their own speed regardless of how fast the line or router is. A five-year-old phone may simply be incapable of pulling 200 Mbps over WiFi.

Contention matters too: background app updates, cloud backups, a console downloading a game, or another household member streaming 4K will all eat into a single test. To get a clean reading, test with just one device active and nothing big running in the background.

If a wired test also comes up short, look at the line itself - though these are less common than WiFi issues:

• ONT and cabling: a loose or kinked fibre patch cable, or an ONT that needs a power-cycle, can throttle everything. Power the unit off for a few minutes and check the cables.
• Peak-hour congestion: speeds can dip in the evening peak (roughly 4pm-10pm) as the neighbourhood loads up. Testing at different times reveals the pattern.
• International vs local routing: overseas sites and undersea-cable faults can slow international traffic while local content stays fast - which is why your test server choice matters.
• Throttling and shaping: genuine throttling on uncapped SA fibre is rare and must be disclosed in the terms, but some plans shape traffic after a fair-use threshold. Compare results with and without a VPN to sanity-check.

It helps to know what "100 Mbps" actually promises. The advertised figure is the line (sync) rate. Real-world throughput is always a little lower once you account for WiFi loss, protocol overhead, device limits and the distance to the test server. A clean wired test landing within roughly 10% of your package speed is considered normal and healthy - you're getting what you pay for.

Work through these in order - the most impactful fixes come first:

1. Test wired to confirm whether it's WiFi or the line.
2. Reboot the ONT and router (power off 30 seconds to a few minutes, ONT first).
3. Move and elevate the router - central, out of cupboards, away from walls, metal and microwaves.
4. Use the 5 GHz band for speed-critical devices; keep 2.4 GHz for far rooms and smart-home gear.
5. Set a clear channel on 5 GHz to dodge neighbour congestion.
6. Pause background hogs - updates, backups - and check for unknown devices on your network.
7. Upgrade to a WiFi 6/6E router or a mesh system for large homes or to escape a weak ISP router.
8. Check for shaping or throttling by comparing tests with and without a VPN, and review your plan's fair-use policy.
9. Contact your ISP with wired speed-test screenshots taken at peak and off-peak so they can log a line fault.
10. Consider an upgrade - if you hit full speed wired but genuinely need more, move to a faster package.

For results you can trust:

• Connect a laptop directly to the ONT/router with Ethernet and make it the only active device.
• Confirm a gigabit link (a green LAN light; orange usually means a 100 Mbps cap) and use an undamaged Cat5e/Cat6 cable.
• Use a reputable tool - our speed test or the Speedtest app - run it several times, and try multiple local servers.
• Disable any VPN, and test at both peak and off-peak times to spot congestion.