You’re paying for a 100Mbps fibre line, but Netflix buffers, video calls stutter and the speed test says 23Mbps. Before you assume your ISP is throttling you, know this: in the vast majority of “slow fibre” complaints we investigate, the fibre line itself is running at full speed. The bottleneck is somewhere between the ONT on your wall and the device in your hand.
Here are the nine causes we see most often in South African homes and offices — roughly in order of how frequently they turn out to be the problem — and how to fix each one.
1. You’re testing over WiFi, not the line
This is the single biggest source of confusion. WiFi speed and line speed are two different things. A speed test run from a phone two rooms away from the router measures your WiFi performance, not your fibre.
Fix: Plug a laptop directly into the router with an Ethernet cable and run the test again. If the cabled test hits your package speed, your line is fine — your WiFi needs attention (see points 2–4). If the cabled test is also slow, keep reading from point 5.
2. Router placement is working against you
WiFi signal degrades dramatically through brick walls, metal geysers, mirrors and fish tanks — and South African homes tend to have a lot of double-brick walls. A router hidden in a TV cabinet at one end of the house cannot deliver full speed to a bedroom at the other end.
Fix: Position the router centrally, elevated, and in open air — not inside a cupboard. If the house is large or has thick walls, a mesh WiFi system or a wired access point will do far more for your real-world speeds than upgrading your fibre package ever will.
3. You’re stuck on the 2.4GHz band
Most routers broadcast two networks: 2.4GHz (longer range, much slower, badly congested in complexes and estates) and 5GHz (faster, shorter range). Older devices — and sometimes newer ones by default — latch onto 2.4GHz, which realistically tops out around 40–60Mbps in a congested environment, no matter how fast your fibre is.
Fix: Connect to the 5GHz network for anything that needs speed. If your router merges both bands under one name, check whether you can split them so you can choose deliberately.
4. Your router is the bottleneck
The free router supplied with a fibre installation five years ago was built for a 20Mbps line. Put a 200Mbps or 500Mbps package behind it and it simply cannot keep up — its CPU and WiFi radios max out long before the line does.
Fix: If your router is more than four or five years old, or only supports WiFi 4/5, a modern WiFi 6 router is one of the cheapest performance upgrades available. Reboot the old one in the meantime — routers that have been running for months develop memory issues that quietly degrade throughput.
5. Something on the network is eating your bandwidth
One device downloading a game update, syncing cloud backups or seeding torrents can consume an entire line. Smart TVs, gaming consoles and cloud backup tools are the usual suspects — and they do it silently in the background.
Fix: Check your router’s client list or traffic monitor for a device with unusually high usage. Schedule large backups and updates for overnight, and use the router’s QoS (Quality of Service) settings to prioritise video calls over background downloads.
6. Neighbours are on your WiFi
If your WiFi password is still the default printed on the router — or it’s been shared freely over the years — you may be sharing your line with more people than you think.
Fix: Change the WiFi password, use WPA2 or WPA3 encryption, and review the connected devices list. Anything you don’t recognise gets removed when the password changes.
7. Your package doesn’t match your usage anymore
A 25Mbps line was generous for one person in 2020. A household of four streaming in 4K, gaming and working from home simultaneously will saturate it daily — and the symptoms (buffering, lag during evenings) look exactly like a fault.
Fix: Count your heavy-usage devices. As a rough rule, budget 25Mbps per simultaneous 4K stream and 10–15Mbps per video call, plus headroom. If your line is consistently maxed out at peak times, an upgrade — not a fault ticket — is the answer. Different fibre networks offer different speed tiers, so it’s worth knowing which fibre network operator serves your street and what packages exist on it.
8. DNS or routing issues make “fast” feel slow
Sometimes the line speed is perfect but browsing still feels sluggish — pages hesitate before loading, even though downloads fly. That’s frequently a DNS problem: the lookup that happens before any page loads is slow, so everything feels slow.
Fix: Switch your router’s DNS to a fast public resolver such as Cloudflare (1.1.1.1) or Google (8.8.8.8) and test again. If specific sites or services are slow while everything else is fast, that can be an international routing or peering issue — worth reporting to your ISP with specifics, because it’s fixable on their side.
9. There’s an actual line fault
Genuine fibre faults do happen: degraded splices after civil works, faulty ONTs, port issues at the exchange. The telltale sign is a cabled speed test that consistently comes in well under your package speed, at all times of day, on more than one device.
Fix: Before logging a ticket, gather evidence — two or three cabled speed tests at different times, noting the results. A support desk with that information can escalate to the fibre network operator immediately instead of walking you through router reboots you’ve already done. This is also where the ISP you chose matters: on open-access fibre, the network is the same for everyone, but how quickly your ISP escalates and communicates is what determines how long you sit without service.
Quick diagnostic: find your bottleneck in 5 minutes
- Cabled speed test — laptop into router via Ethernet. Full speed? Problem is WiFi (points 2–4). Slow? Continue.
- Reboot the ONT and router — power both off for 30 seconds, test again.
- Check for bandwidth hogs — router client list, pause suspicious devices, test again.
- Test at a different time — slow only at 7–9pm suggests a saturated package or congestion; slow always suggests a fault.
- Still slow on cable, all day, after reboots? Log it with your ISP, with your test results attached.
Frequently asked questions
Does my ISP throttle my fibre speed?
On uncapped, unshaped fibre packages from reputable South African ISPs — no. Genuine throttling is rare; what feels like throttling is almost always WiFi limitations, package saturation or a line fault. Some budget packages are openly “shaped” or “prioritised”, which is disclosed in the product terms — check what you signed up for.
Why is my fibre slow only at night?
Evening slowdowns (roughly 7–10pm) usually mean either your own household is saturating the package at peak usage, or — less commonly — the ISP’s upstream capacity is congested. A cabled speed test during the slow period tells you which: if it matches your package speed, the problem is inside your home.
Will upgrading my fibre package fix slow WiFi?
No. If WiFi is the bottleneck, a faster package changes nothing — the WiFi will still cap out at the same speed. Fix coverage first (router placement, mesh, WiFi 6), then upgrade the line if you’re genuinely saturating it.
How much speed do I actually need?
For most households: 50Mbps covers a couple with moderate streaming; 100Mbps suits a family of four with 4K streaming and remote work; 200Mbps+ is for heavy households, gamers who want fast downloads, and content creators uploading large files.
Still stuck after running through this list? Simplicity Internet Solutions provides fibre on Openserve, Vumatel, Frogfoot, MetroFibre, DFA and LinkLayer networks nationwide — with a support desk that actually diagnoses instead of reading a script. Get in touch and we’ll find your bottleneck.