alkali cleaner

[beau]

What is a common name for an alkali cleaner I can use to clean my RO membrane and at what rate per gallon should I use

[Tellie]

The common name for alkali cleaner is alkali cleaner. But first before you clean a membrane you need to determine what needs to be cleaned. Is it scale, biofoul, organic, or silicates. Alkali will clean organics but not the others. You don't give enough information as to why you want to clean your membrane but in my experiance once a membrane is determined to be fouled on a boat based system it's usually time to just replace it. Cleaning agents are better used on large commercial RO systems that run all the time and have regular cleaning maintenance schedules. If you have ruled out all other causes and believe the higher pressures are from membrane restriction then give it a try it can't hurt. But check with your units manufacturer as to whether they insist on using their cleaners and heed their advice. Using one manufacturers chemicals on another unit can void warranties and led to major and expensive problems. This is not the place to try and save $20.

[beau]

Thank you for your comments.
I put together a DIY watermaker using a 6.5 hp gasoline powered pressure washer (3 gallons a minute flow rate) I am using 2x 40 inch Film Tec membranes. The unit works well and we flush with fresh water.
I am currently in Sorong Indonesia the salt water here is very warm and I am concerned about organic build up in the membranes. Flow rate of fresh water is OK but I want to make sure it stays that way. We use the unit twice a week.
I do occasionally soak the membranes with Sodium Metabisulphite.
Everything is so hard to obtain here as nobody speaks English and I want to make sure we have everything needed on board before continuing our trip.

[Tellie]

Sodium Metabisulphite is meant as a storage solution when you're going to leave your watermaker unused for any length of time. It doesn't do much for cleaning the membrane. In the warmer climes fresh water flushing after each use is more important and the fact that you are using the unit twice a week should be plenty of use to keep the membranes in good condition. If you don't use it twice a week occasionally just keep the twice a week freshwater flush routine and you'll be fine. I know many manufacturers say once a week is OK. But in the warmer waters those that do it twice a week have far less fouling problems. Stuff can grow practically over night inside a dark warm watermaker.

[mrm]

As it is a DIY unit and warranty is of no concern, you may try to use a solution of NaOH (sodium hydroxide) or KOH (potassium hydroxide). Pure chemicals are usually available in laboratory supply shops, but slightly impure ('technical') forms are the main (and often the only) ingredients of drain cleaners, obtainable mostly everywhere.

If you go this route and start to prepare your own alkali cleaner solutions there are some points to consider:

1. wear eye protection as a minimum! alkali burns are nasty.
2. it is up to you to determine the compatibility of materials used to build the watermaker with strong alkali solutions, as well as the proper strength of the solution.
3. in dry form both hydroxides are strongly hygroscopic and they also react with carbon dioxide from air. If you decide to stock on those, store in good sealed containers.