Water salts additions in the fermenter.

Last brew day I completely screwed up my water salts additions. I completely forgot to add my boil kettle additions, and didn't realize it until after I had everything in the fermenter, and fermentation had started.

I chose to draw off a cup of wort, boil it and add the salts to dissolve them, I chilled it and tossed it back into the fermenter, and stirred it well.

Any problems with this method?

I don't see any problem with it but, OTOH, I don't see that it would do much good depending on the objectives of the additions. If, for example, you intended to lower kettle pH by addition of additional calcium obviously adding them in the fermenter will not achieve that goal. If, as another example, the intention was to add zinc for yeast health then you would be successful adding it to the fermenter. Then again if you were following guidance from one of those spreadsheets that advise chalk or bicarbonate additions you would have saved yourself the problems that this would cause in the kettle but will still have the problems it will cause in the fermenter.

I was trying to achieve Mosher's IPA water, but with lower SO4, which according to the spreadsheet I used was exactly what I wanted, however, my concern once everyhting was in the fermenter became yeast health. According to my additions in the mash, I was still very low on calcium and magnesium, so that is why I decided to ad the salts to the fermenter.

I also realized I didn't add enough of my salts to the mash, however I did use 5.2 buffer, so I am glad I did that at the very least. According to my spreadsheet, pH would have been 5.02 with all salts added, so I'm hoping the buffer helped.

I am going to have to brew this recipe again without all of the mistakes, and compare them side-by-side. I'm sure I will still have good beer, but I did kick myself in the pants when i realized I forgot the kettle salts additions.

Live and learn, usually, I only make the same mistake once.

Of course I have no idea what water you are starting from nor how much of what you had planned to add but it is unlikely that you would realize pH 5.02 from salt addition alone. It is also unlikely that 5.2 would have much of an effect. Supplementing calcium and magnesium in the fermenter can't hurt but bear in mind that malt is about 0.5% magnesium by weight and contains a fair amount of calcium as well. Several commercial beers are brewed with water with very low calcium and magnesium leves.

How long ago was "last brew day"? There's a good chance it's too late to do much good. I've brewed some mighty tasty beer that I forgot to salt.

I brewed this past monday, and I already added the boil kettle additions to the fermenter, by dissolving them in a cup of wort that I boiled and chilled.

I used 100% RO water.