Black spots in tub?

Ithacarun5

Member
Nov 8, 2019
10
Tampa
Hello, bought a used 2 person 130gallon hottub. Ran spa cleaner line flush for 3 cycles, emptying the tub each cycle. Wiped the shell down with bleach. Filled it for my final fill, balanced the alkalinity, pH, hardness, then added my bromine granules and tabs. Levels were good, bromine bank solid, added my shock (MPS) then the next morning a few black spots formed on the walls. I drained it, and they don't wipe off with bleach and a paper towel, but they wipe easily off with muriatic acid and a paper towel. Algae? Iron? I am using well water that is prefiltered before the tub. I did 3 cycles with the line flush, and the only sludge of any sort were these red foam/flakes that I'm assuming is due to the high iron. Do I have an algae issue or a metal issue? This is my first tub, so I'm a rookieIMG_20191029_164804.jpgIMG_20191029_164813.jpg
 

Mendy48

Bronze Supporter
Apr 27, 2018
737
Midland, MI
Welcome to the forum. I've never seen anything like that before, but I'll let an expert chime in here shortly. Could you add some information about your tub in your signature. It will help in diagnosis your issue here. See mine for example. I'm thinking it could be Cobalt Staining, but there's no guarantee. Interesting to see what this could be though. Click here to see a thread about this.

Out of curiosity, are you testing your tub with your own testing kit. If so, what type of testing kit to you have. You mentioned that you added bromine granules and tabs and MPS? I'll let someone chime in here about those chemicals. I've haven't used bromine or MPS before.
 

Mendy48

Bronze Supporter
Apr 27, 2018
737
Midland, MI
Oh! Yeah! You want to stay away from test strips. You will need to invest in your own test kit. Get your test kit (TF-100 or Taylor K-2006C). We recommend the TF100 from TFTestKits.net or the Taylor K-2006C. See Test Kits Compared. I suggest the TF-100. A proper test kit is needed to get the accurate water chemistry results needed to follow the TFP protocols.

Once you get your test kit, post your results here (CC, TA, FC, CH, pH & CYA). Don't forget to add your signature to your profile.

An expert will chime in here shortly with our stain question...