The Summer to Learn my Water Maker & Its Media Filter

Ophelia came equipped to me with an AquaMatic 900 GPD Watermaker.  I made a goal for this summer to learn how to run and troubleshoot the system.  It is a somewhat complex system (at least to me), with 8 various filters, a Media (sand) filter and a single RO Membrane. Specifically, I wanted to change out the sand in the media filter, since it probably had not been done in 6 or 7 years. All the other filters have been changed annually by me, since 2017.

One interesting find, in reading the operation manual, is that it clearly states “one should use EITHER the Plankton Filters or the Media Filter, but not both.”  Of course my set up arrived to me, with both filters plumbed in!  This may be causing the boost pump to struggle a bit.  I am hoping that since the entire set up worked for the prior owner for the last 20 years, I might as well keep it and see what I can learn, before removing anything.


The Media Filter is an interesting set up that lets the sea water run thru a layer of gravel, followed by a finer sand. Stuff in the water gets trapped by the gravel & sand.  Theoretically, this filter is an easy clean, by using the backflush valves & a bucket.  I wanted to establish a baseline, by removing it, changing out the gravel & sand & reinstalling it.  So the first order of business was to get the fiberglass Media Filter (“Vessel”) out of the boat and onto the dock!

From the above schematic, you can see that the Vessel is plumbed in with grey Schedule 80 PVC pipe & fittings.  The Inlet side was easy to unscrew.  The Outlet side was glued closed and I had to cut the PVC piping out, in order to free the filter for removal. I was surprised how heavy the filter is.  The extremely limited data in the manual indicates that the media vessel should hold 15 lbs of gravel base and about 26 lbs of sand.  Add in the weight of the sea water combined with a very tight lazaret and it was somewhat difficult to remove. However, I got it onto the dock & cleaned out the old sand with a hose and the help of Baer, my son.  We then used two separate 5-gallon buckets (one for gravel and another for Micro-Z) to thoroughly wash & rinse the new media, before going into the Vessel. The old sand was filthy & there was no base gravel, so I am glad that I did a full tear-down!  It took about 30 mins of flooding & rinsing the media with a carbon filtered dock hose, to get all the gravel & micro-z cleaned up!



Baer helped me carefully measure the 15 lbs of base gravel and get it into the fiberglass media filter (Vessel).  We used a plastic cup and were careful to set the height for the center stand-pipe, so it can fit into the top properly.  For the sand, we used a product called Micro-Z, which was recommended to me by some smarter people on the NOG!  Micro-Z is a:

“High quality, granular, zeolite filter media that replaces conventional multimedia. It is produced from a unique mineral deposit having high surface area & porosity.  The surface structure of Micro-Z features microscopic mineral projections that allow particulate matter to penetrate deeply in the bed.  The properties make Micro-Z and ideal filtration Media”

Once the Vessel was properly filled up with the new gravel & Micro-Z, I put it back into its hole in the laz.  The next step was for me to learn about PVC fittings, so that I could re-plumb the outlet side.  After striking out at Home Depot, I was told to try a local shop called McArdle & Walsh, who stock all the gray schedule 80 PVC fittings!  All my piping is ¾ inch.  I brought to them the parts I cut out and they helped me duplicate the fittings. Specifically, I needed 2 Couplings (NPT threads), a 90-degree Elbow, a Union, and about 6 inches of new pipe.  They also sold me the Primer & the correct Cement.  After watching a few youtube clips, I learned to chamfer the edges, clean them up with light sandpaper, prime them, apply the cement and fit them together quickly, with no more than a ¼ turn. The end result should be a very strong chemical bond that (hopefully) won’t leak!  So far, I ran only the fresh water flush for about 30 mins, to fill up the media filter and to try to purge the air out.  Next Step will be to run the boost pump, before we try to make water!
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