Every time I come back from martial arts class, I wash my Gi. I put it in with all whites and use Tide Bleach Powder; which I figure is not real bleach. My Gi never comes out of the wash perfectly white and I am afraid to use hot water as I heard that this shrinks a Gi. How do Japanese keep their Gi's so perfectly white?

People that train a lot here seem to have off white gi
I believe it is the sweat that stains it

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if you go several times a week invest in another one or two. This means each is washed less and the risks are reduced. With mine, I use vanish wash powder, but I think anything with "oxy action" works really well as it comes out near shiny! Hope to have helped.

Doumou arigatou gozaimashita.

I found the use of oxyclean a great use for my gi. I just soak the gi in a bucket for a few hours and then wash it in the washing machine. The oxyclean keeps the stubborn dirt out of the gi and makes washing it a much easier task.

If I may be so humble as to offer an alternative suggestion:

If it is badly stained with that ugly "yellow" that many gi have after a being washed following many vigorous classes, soak it in white vinegar (I'm talking a gallon in a full washing machine)for 2 hours.

Let the machine complete its cycle. Once it is complete, wash it as you would usually, but do this one thing: add hydrogen peroxide with your regular wash detergent, liquid or powder makes no difference. I recommend no more than 1.5 cups per washing machine load, but please use your own descretion based on the results you get.

DO NOT PUT THE GARMENT IN THE DRIER! Hang it to dry. Whatever you do, do NOT put your gi in the drier. Not only do you risk shrinkage, you are emphasizing whatever yellowing there is already. If you have washed it according to the instructions above, you may also undo everything you've just done.

Fold it neatly and put it in your equipment bag, or hang it up in the closet, your choice, whatever.

You may need to repeat this process a couple of times to get that "sharp" whiteness. Also, if you have hard water where you are, you may want to invest in a water softening device. Not only will your gi thank you, but you will notice a big difference in everything else.

I wish you success.