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                                                                    EXHIBIT 99.3
 
                           PCI CHEMICALS CANADA INC.
 
                               OFFER TO EXCHANGE
                   UP TO $175,000,000 IN PRINCIPAL AMOUNT OF
            9 1/4% SERIES A SENIOR SECURED NOTES DUE 2007 ISSUED AND
                          SOLD IN A TRANSACTION EXEMPT
                   FROM REGISTRATION UNDER THE SECURITIES ACT
                              OF 1933, AS AMENDED
                                      FOR
                      $175,000,000 IN PRINCIPAL AMOUNT OF
                 9 1/4% SERIES B SENIOR SECURED NOTES DUE 2007
 
To Our Clients:
 
     Enclosed for your consideration is a Prospectus dated January   , 1998 (as
the same may be amended or supplemented from time to time, the "Prospectus") and
a form of Letter of Transmittal (the "Letter of Transmittal") relating to the
offer (the "Exchange Offer") by PCI Chemicals Canada Inc. (the "Company" and,
together with Pioneer Americas Acquisition Corporation ("PAAC") and the other
subsidiaries of PAAC, the "Issuers") to exchange up to $175,000,000 in principal
amount of its 9 1/4% Series A Senior Secured Notes due 2007 issued and sold in a
transaction exempt from registration under the Securities Act of 1933, as
amended (the "Original Notes"), for $175,000,000 in principal amount of its
9 1/4% Series B Senior Secured Notes due 2007 (the "Exchange Notes").
 
     The material is being forwarded to you as the beneficial owner of Original
Notes carried by us for your account or benefit but not registered in your name.
A tender of any Original Notes may be made only by us as the registered holder
and pursuant to your instructions. Therefore, the Issuers urge beneficial owners
of Original Notes registered in the name of a broker, dealer, commercial bank,
trust company or other nominee to contact such registered holder promptly if
they wish to tender Original Notes in the Exchange Offer.
 
     Accordingly, we request instructions as to whether you wish us to tender
any or all Original Notes, pursuant to the terms and conditions set forth in the
Prospectus and Letter of Transmittal. We urge you to read carefully the
Prospectus and Letter of Transmittal before instructing us to tender your
Original Notes.
 
     Your instructions to us should be forwarded as promptly as possible in
order to permit us to tender Original Notes on your behalf in accordance with
the provisions of the Exchange Offer. The Exchange Offer will expire at 5:00
p.m., Eastern Standard Time, on               ,      , 1998, unless extended
(the "Expiration Date"). Original Notes tendered pursuant to the Exchange Offer
may be withdrawn, subject to the procedures described in the Prospectus, at any
time prior to the Expiration Date.
 
     If you wish to have us tender any or all of your Original Notes held by us
for your account or benefit, please so instruct us by completing, executing and
returning to us the instruction form that appears below. The accompanying Letter
of Transmittal is furnished to you for informational purposes only and may not
be used by you to tender Original Notes held by us and registered in our name
for your account or benefit.
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                                  INSTRUCTIONS
 
     The undersigned acknowledge(s) receipt of your letter and the enclosed
material referred to therein relating to the Exchange Offer of Pioneer Americas
Acquisition Corp.
 
     THIS WILL INSTRUCT YOU TO TENDER THE PRINCIPAL AMOUNT OF ORIGINAL NOTES
INDICATED BELOW HELD BY YOU FOR THE ACCOUNT OR BENEFIT OF THE UNDERSIGNED,
PURSUANT TO THE TERMS OF AND CONDITIONS SET FORTH IN THE PROSPECTUS AND THE
LETTER OF TRANSMITTAL.
 
Box 1  [ ]  Please tender my Original Notes held by you for my account or
            benefit. I have identified on a signed schedule attached hereto the
            principal mount of Original Notes to be tendered if I wish to tender
            less than all of my Original Notes.
 
Box 2  [ ]  Please do not tender any Original Notes held by you for my account
            or benefit.
 
Date:             , 1998
 
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                                                      Signature(s)
 
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                                        ----------------------------------------
                                               Please print name(s) here
 
Unless a specific contrary instruction is given in a signed Schedule attached
hereto, your signature(s) hereon shall constitute an instruction to us to tender
all of your Original Notes.
 
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