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                                                                    EXHIBIT 99.4
 
                           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 Securities Dealers, Commercial Banks
  Trust Companies and Other Nominees:
 
     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").
 
     We are asking you to contact your clients for whom you hold Original Notes
registered in your name or in the name of your nominee. In addition, we ask you
to contact your clients who, to your knowledge, hold Original Notes registered
in their own name. The Issuers will not pay any fees or commissions to any
broker, dealer or other person in connection with the solicitation of tenders
pursuant to the Exchange Offer. You will, however, be reimbursed by the Issuers
for customary mailing and handling expenses incurred by you in forwarding any of
the enclosed materials to your clients. The Issuers will pay all transfer taxes,
if any, applicable to the tender of Original Notes to it or its order, except as
otherwise provided in the Prospectus and the Letter of Transmittal.
 
     Enclosed are copies of the following documents:
 
     1. The Prospectus;
 
     2. A Letter of Transmittal for your use in connection with the tender of
        Original Notes and for the Information of your clients;
 
     3. A form of letter that may be sent to your clients for whose accounts you
        hold Original Notes registered in your name or the name of your nominee,
        with space provided for obtaining the clients' instructions with regard
        to the Exchange Offer;
 
     4. A form of Notice of Guaranteed Delivery; and
 
     5. Guidelines for Certification of Taxpayer Identification Number on
        Substitute Form W-9.
 
     Your prompt action is requested. 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.
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     To tender Original Notes, certificates for Original Notes or a Book-Entry
Confirmation, a duly executed and properly completed Letter of Transmittal or a
facsimile thereof, and any other required documents, must be received by the
Exchange Agent as provided in the Prospectus and the Letter of Transmittal.
 
     Additional copies of the enclosed material may be obtained from United
States Trust Company of New York, the Exchange Agent, by calling (800) 548-6565.
 
     NOTHING HEREIN OR IN THE ENCLOSED DOCUMENTS SHALL CONSTITUTE YOU OR ANY
PERSON AS AN AGENT OF THE ISSUERS OR THE EXCHANGE AGENT, OR AUTHORIZE YOU OR ANY
OTHER PERSON TO MAKE ANY STATEMENTS ON BEHALF OF EITHER OF THEM WITH RESPECT TO
THE EXCHANGE OFFER, EXCEPT FOR STATEMENTS EXPRESSLY MADE IN THE PROSPECTUS AND
THE LETTER OF TRANSMITTAL.
 
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