Doubled in size in minutes

Bleach can be corrosive to the metal.

https://www.cemag.us/article/2014/09/are-your-stainless-steel-surfaces-being-corroded-repeated-bleach-use

Are Your Stainless Steel Surfaces Being Corroded by Repeated Bleach Use?
Wed, 09/17/2014 - 3:17pm 2 Comments
by Wendy Hollands and Jay Postlewaite, Ph.D.
Abstract

Bleach is known to be corrosive to metals that are commonly found in pharmaceutical, bioprocessing, and medical device work environments. Two commonly used types of stainless steel coupons were exposed to household bleach and sodium dichloroisocyanurate (NaDCC) solutions over a period of eight weeks. The rate and degree of corrosion exhibited by the stainless steel coupons were compared. Bleach diluted at 1:10 and 1:50 showed corrosion of the stainless steel. Coupons exposed to NaDCC solutions at levels of 187 and 937 ppm active chlorine did not show corrosion, suggesting that NaDCC can serve as an effective alternative disinfectant to liquid bleach.

Introduction

Liquid bleach (sodium hypochlorite solution) is used as a disinfectant in pharmaceutical, bioprocessing, and medical device facilities commonly at a 1:10 dilution (one part bleach combined with nine parts water). However, bleach is known to be corrosive to metals and can cause damage to some plastics. Even with these drawbacks, bleach is commonly used because it kills a large spectrum of microbes, is widely available, and is easy to use. Sodium dichloroisocyanurate (NaDCC) is a bleach alternative available in a solid tablet form. It also kills a large spectrum of microbes, is widely available and is easy to use.

Objective

The objective of this study is to compare the corrosion caused by bleach and NaDCC solutions at various concentrations on two common types of stainless steel surfaces and to demonstrate the advantages of using NaDCC over bleach as part of a disinfection program.

Procedure
For this study, 18 stainless steel 316 (316) and 18 stainless steel 304L (304L) 2” x 2” x 1/8” coupons were obtained from GlobePharma. Six solutions were prepared daily with deionized water (18 MΩ RODI) using commercially available Clorox® bleach and commercially available tablets containing NaDCC. The solution concentrations, formulations and appearance are compiled in Table 1.

Table 1. Test solution formulations used in the corrosion study.
Table 1. Test solution formulations used in the corrosion study.
Three coupons were submerged in 400-mL beakers containing 250 milliliters of one solution listed above ensuring complete coverage of the coupons. The beakers were then covered with plastic wrap. The coupons were removed from the beakers daily and wiped dry for visual inspection. Any differences were documented (Table 2) and photographed, as shown in Figures 1 - 17. Noted differences include changes in color, rust and corrosion, pitting, gas evolution while the coupons were submerged in solution, and metal deposition on the glass surface of the beaker.

This is defiantly not corrosion. This is black spores and it spread over night rapidly.

Vinegar! I got desperate. Ran around my house asking my self what might be the opposite of bleach. I decided to try vinegar. Poured some on, it all disappeared immediately. No idea what it was/is. But vinegar seems to be working

Good to know you solved the problem.