What causes slime or gunk in my hot tub pipes?
- Thread starter Zephyr
- Start date
Freddie
Member
That sounds like biofilm it forms inside the plumbing when bacteria stick to the pipes. Even if sanitizer levels look good the film protects bacteria from being killed. Try using a line flush product like AquaDoc Spa Purge before your next drain and refill. Let it circulate for a few hours then drain, rinse and refill fresh.
Manikshaw
Member
Agree it’s most likely biofilm. I had the same issue and couldn’t figure it out for months. Regular sanitizer doesn’t touch it. You’ll need to run a system flush to break it down. After cleaning keep your sanitizer at the upper range for a few days so it doesn’t come back.
syedsam
Member
Sometimes old filters hold onto that gunk too. If they’ve been in use for a while replace them after doing the line flush. I do a deep clean with AquaDoc Filter Cleaner every month and haven’t had that slimy feeling since.
Oscar Ricci
Member
It’s probably biofilm building up in the pipes from bacteria. Try using a line flush product like AquaDoc Spa Purge before your next drain and refill, and let it circulate for a few hours.
Temi Mwangi
Member
I’ve seen that, and yeah, it usually means there’s buildup in the plumbing (like biofilm) so it keeps coming back when you run the jets. The most effective move in my experience is a spa purge/line flush before you drain, run the jets for a few hours, then drain and rinse. After the refill, I shock and keep sanitizer a little on the high side for a few days to knock out what’s left. If your filter is older, swap it too, because filters can “hold onto” that gunk and bring it right back.
ManeuverWise
New member
I agree on the purge, I had to do that last year to finally get rid of some nasty slime. One thing that actually kept it from coming back for me was adding aquadoc's enzyme stuff every week. It basically eats the oils and gunk before they can even turn into biofilm in the pipes. If you're going through the trouble of a deep clean and fresh fill, it's worth tossing some in so you don't have to do it again in two months.
Amber Chase
Member
Yeah, that gunk almost always means there’s buildup inside the plumbing, not something you’re doing wrong on the surface. I dealt with this last year and it drove me nuts because sanitizer levels looked fine and filters were clean, but every time I hit the jets, slimy bits would show up again. Warm water, high bather load, body oils, lotions, all that stuff slowly coats the inside of the pipes and turns into biofilm. Once it’s established, normal chlorine or bromine can’t really penetrate it.
What finally worked was accepting that it needed a proper purge. I ran aquadoc spa purge before draining, cranked all the jets, and let it circulate for a few hours. The amount of brown foam and stringy junk that came out was gross but also confirmed where the problem was hiding. After draining, I rinsed the shell, wiped around the jets, refilled, then balanced alkalinity first so pH wouldn’t bounce all over the place. After that, sanitizer actually held instead of disappearing in a day or two.
To keep it from coming back, I changed my habits a bit. I don’t ignore early signs anymore, like that slick feeling or sanitizer demand jumping fast. I also keep the cover cracked after use so things can dry, and I stay on top of weekly maintenance instead of waiting for it to look bad. Once the biofilm is gone, the tub is way easier to manage. The key lesson for me was clear water doesn’t mean clean pipes, the jets will always tell the real story.
What finally worked was accepting that it needed a proper purge. I ran aquadoc spa purge before draining, cranked all the jets, and let it circulate for a few hours. The amount of brown foam and stringy junk that came out was gross but also confirmed where the problem was hiding. After draining, I rinsed the shell, wiped around the jets, refilled, then balanced alkalinity first so pH wouldn’t bounce all over the place. After that, sanitizer actually held instead of disappearing in a day or two.
To keep it from coming back, I changed my habits a bit. I don’t ignore early signs anymore, like that slick feeling or sanitizer demand jumping fast. I also keep the cover cracked after use so things can dry, and I stay on top of weekly maintenance instead of waiting for it to look bad. Once the biofilm is gone, the tub is way easier to manage. The key lesson for me was clear water doesn’t mean clean pipes, the jets will always tell the real story.
Katherine Morgan
Member
I dealt with this last year and yeah, that slimy stuff is almost always coming from inside the plumbing, not the filter or the water you’re testing. What’s happening is oils, sweat, lotions, and whatever else comes off bathers slowly coat the inside of the pipes. Bacteria stick to that layer and form biofilm. Once it’s there, normal sanitizer doesn’t really touch it, even if your readings look fine.
That’s why it keeps coming back a few days later. You turn on the jets, pressure changes, and little chunks break loose. I kept shocking and cleaning filters at first and it did nothing. The only thing that actually fixed it was doing a proper purge before draining. When I ran aquadoc spa purge and cranked all the jets, the tub started spitting out brown foam and stringy gunk I didn’t even know existed. Not pleasant, but it explained everything.
After draining and refilling, I noticed sanitizer demand dropped a lot and the slick feeling never came back. To keep it from returning, I stay ahead of it now. I don’t let pH drift all over the place, I watch bather load, and I don’t ignore early signs like that faint slime or sanitizer disappearing faster than usual. Clear water can lie, the pipes don’t. If the jets are talking, it’s worth listening early instead of fighting it for months.
That’s why it keeps coming back a few days later. You turn on the jets, pressure changes, and little chunks break loose. I kept shocking and cleaning filters at first and it did nothing. The only thing that actually fixed it was doing a proper purge before draining. When I ran aquadoc spa purge and cranked all the jets, the tub started spitting out brown foam and stringy gunk I didn’t even know existed. Not pleasant, but it explained everything.
After draining and refilling, I noticed sanitizer demand dropped a lot and the slick feeling never came back. To keep it from returning, I stay ahead of it now. I don’t let pH drift all over the place, I watch bather load, and I don’t ignore early signs like that faint slime or sanitizer disappearing faster than usual. Clear water can lie, the pipes don’t. If the jets are talking, it’s worth listening early instead of fighting it for months.
Ethan Wells
Member
Most of the big causes are already covered here, but one angle that helped me understand why it keeps coming back is how little circulation some plumbing actually gets day to day.
A lot of tubs have dead legs and air lines that barely see sanitizer unless the jets are on full. Oils and sweat stick there first, then bacteria builds a slime layer that basically shields itself. So even if your sanitizer tests fine in the main body of water, those low-flow sections are living in a totally different world. Every time you hit the jets, pressure changes and bits of that stuff get knocked loose, which is why it feels like it “reappears” out of nowhere.
One thing that reduced how fast it returned for me, even before doing a full purge, was changing how I run the tub. I started doing a daily short jet run with all diverters open, not just the zone we usually sit in. I also paid attention to pH drift, because when pH climbs from aeration, sanitizer gets less effective right where biofilm likes to live. Once I kept alkalinity steady and stopped letting pH bounce, the slime showed up way slower.
So yeah, it does mean buildup inside the plumbing, but it’s not just a cleanliness issue, it’s a circulation and chemistry interaction thing. Pipes that don’t get flow are always the first to get gross. Anyone else notice the air-only jets are usually the worst offenders?
A lot of tubs have dead legs and air lines that barely see sanitizer unless the jets are on full. Oils and sweat stick there first, then bacteria builds a slime layer that basically shields itself. So even if your sanitizer tests fine in the main body of water, those low-flow sections are living in a totally different world. Every time you hit the jets, pressure changes and bits of that stuff get knocked loose, which is why it feels like it “reappears” out of nowhere.
One thing that reduced how fast it returned for me, even before doing a full purge, was changing how I run the tub. I started doing a daily short jet run with all diverters open, not just the zone we usually sit in. I also paid attention to pH drift, because when pH climbs from aeration, sanitizer gets less effective right where biofilm likes to live. Once I kept alkalinity steady and stopped letting pH bounce, the slime showed up way slower.
So yeah, it does mean buildup inside the plumbing, but it’s not just a cleanliness issue, it’s a circulation and chemistry interaction thing. Pipes that don’t get flow are always the first to get gross. Anyone else notice the air-only jets are usually the worst offenders?