Re: Back to the GE Merlin.

Are you saying that you are getting a product water of H 3.2 out of the RO to your tank?

If so, you will need to buffer it to at least pH 4.5-5.0 before adding it to the tank.

Now, I would measure the pH of the tap and of the RO output without the cation resin....I would also measure the TDS and/or (at least) hardness. The softer your tap and RO output, the less resin (if at all).

This system has worked well for me at 250-350 ppm tap rendering anywhere from 40-100ppm product on used membranes (after a few months).

On the other hand, Mike has not had the same results, though now he has upgraded to a larger softener. Mine is a simple cartridge and actually I have not used it in several months.

God listens. He may not always give you everything you want, when you want it; but he always gives you what you really need, when you need it most!

Re: Back to the GE Merlin.


no the water goes from the cation resin into the merlin carbon cartridge with a ph of 3,2
the thing i was wondering is if it can damage the merlin membranes..

without the resin in the prefilter i end up at ph 6,2 and 16 uS from only the merlin
normal tap water has a ph of 7 and a tds of 700 uS

the setup i was using was like this
from the tap to the prefilter with a carbon cartridge
then to the second stage of the prefilter cation resin (wich made the water very acid 3,2ph
then to the merlin and then to a resin silicate filter before the product water goes into my water barrel
the end product had a ph of 5,5 and a tds of 0

like i wrote before the only thing i,m worried about is if the acid water from the cation resin can damage the membranes of the merlin

Re: Back to the GE Merlin.

Hi, I feel like a bit of my experience may be valuable here. I don't see a minimum or a maximum pH value in any of the paperwork so I'm not going to be any help with your pH problem. If your tap is 700uS that would make it approximately 450ppm TDS. If it's mainly calcium and magnesium like mine is the small softener will need regenerated much much much too often. You'll know if it's failed in 6 months if your product water is high in uS/TDS.
To give you an idea of how often the resin needs regenerated my water is also around 400ppm TDS and I could exhaust the small softener in a single large water change. My water is really high in calcium/magnesium/iron so your experience could be more similar to Ed's and this setup may work for you. If you are really worried about your membranes keep an eye on your us/TDS. If the softener can't keep up your numbers will continue to rise even with regular regeneration of your resin.

Re: Back to the GE Merlin.

I agree with Mike, but I think your solution could be as simple as placing the silicate resin after the cation and before the RO Unit. You should try this and let us know how it goes. I have never used a silicate resin so my recommendation simply follows the logic of what you described. In any case, being you, I would not worry as most TFC membranes will easily handle pH 3-4 and this actually will help maintain a cleaner membrane for a longer time which is the idea behind RO pretreatment. pH 1-2 is used for membrane cleaning and defouling.
God listens. He may not always give you everything you want, when you want it; but he always gives you what you really need, when you need it most!

Re: Back to the GE Merlin.

i,ve now have this setup and it works great

first tap water going to carbon prefilter then to the cation resin prefilter
after that to the the merlin and after that the product goes through a silicate filter
this gives me perfect water tds 03 and with a ph of 5,2

Re: Back to the GE Merlin.

The Merlin being a high output semi commercial unit is generally less restrictive than units using low output membranes > 150<).
10% or less of your feed tap water hardness would be about right from a Merlin membrane (Dow Filmtec TLC-350) after it has been working for a few months.
Then, your fish (South American blackwater habitat), don't live in 0ppm water... even if it is very soft.
I would start worrying about flushing when the output exceeds 30% of the feedwater hardness. Still at this point you can continue using it until you can buy a new set of membranes.
Ideally, you should use softening resin, cati, ani or both (if you want distilled water quality) before the membrane. Best is separate cation and anion resins, though I use only cation. I don't like to strip my water completely.
Here you have a few links that may be of interest. ... sh-Kit.pdf

When I have found the need to flush I have used a different method (I don't have a flush kit) and maybe not too efficient. The science behind flushing is simple, to dissolve excess hard ion alts that are saturating the membrane and flush them out. I prepare a pH 1.5 (+/-) solution using regular HCL solution (muriatic acid as sold at HD or Lowe's or your local pool store) and RO water, and then I take out my membranes, fill the sumps with the pH 1.5 solution, put the membranes back in and tighten the sumps to where they should be and allow them to soak for up to 24 hours. The solution should be warm, around 100F or a bit more when you fill the sumps.
You can additionally rig up a recirculation pump and bucket (a clean 5 gallon bucket works just fine) to circulate the solution through the membranes. This will shorten flush time very much and give better results. The recirc pump does need to be able to pressurize at least up to 40psi.

I'm sure a flush kit would make your life much easier if you want to flush, but me, I've gotten lazy, have always polished my RO feedwater BEFORE it hits the membrane. I can recharge my resins (I don't use mixed bed) for years and since 2007 I'm only on my second pair of Merlin membranes and still they have a long way to go.

All this said, it all depends on where you live and your municipal tapwater supply. You might also ask Mike Troxell (19Ghost79) or Dr. Dennis Chang (Califish) on their experiences in Las Vegas.

I live in SLC and though our water here is generally hard, I live in an area where we have the benefit of the Jordan Valley Water Conservancy District which is very well treated and of a very high quality from the source in the Wasatch and Uinta Mountain snow pack. ... tml?pg=all
Lucky me.

Good luck and yeh!...don't be so picky.. 22 ppm? I'm happy at 60ppm!

God listens. He may not always give you everything you want, when you want it; but he always gives you what you really need, when you need it most!