Odd algae

[nfras]

When cleaning the tank the other day I noticed a buildup of white algae around the in-tank thermometer. When I rinsed the thermometer it came off in great lumps. I have also noticed it building around the suctions cups on the heater and termperature probe. Any ideas what it could be?
Tank chemistry is
ammonia <0.1ppm
pH 6.6 - 6.8
nitrites neglible

[Fishguy2727]

I have seen deposits on heaters and other equipment with certain rubbers and plastics, especially if they were once in use, put in storage for a while (dried off), and then used again. There is no white algae. I'm not sure what this is but it never seems to bother my fish, it's just an eyesore.

[nfras]

Thanks reptileguy. It's realy ugly and a bit of a bugger to clean. Ah well.

[CJ1]

Mineral deposits from your tap water.