RO troubleshooting

[johnzillmer]

Wonder if anyone has had the experience I am having:

I run a pieced-together RO system (Kent 50gpd membrane in an old 24gpd housing, two catalytic carbon prefilters from Filter Guys for chloramine removal, and a carbon-block/particulate prefilter of the sort used on TFC bare-bones setups). Membrane is at least 5 years old, used pretty lightly. I got about 5 years out of the previous membrane.

Experienced slime algae in the reef tank, so I tested the RO for PO4 -- found none. Purchased and hooked up a TDS meter, and found that the source water is about 90ppm (Minneapolis city water), the RO water is 1-2ppm, and (oddly) the stored RO water (which was in a plastic trash can) tested at 7ppm. I figured the trash can was leaching something, so I removed it from use.

Further playing with the TDS meter reveals that the RO water is 1-2ppm only after the unit has been running for a couple of minutes. The first couple of cups of RO water that are produced after starting up the unit (I have no float switch, but instead just turn off the source water manually when my bucket is full) test at approximately 50ppm, then slowly drop to 1-2ppm.

I wonder why this happens. Any ideas? How could all that TDS get through the membrane while it is sitting? For now, I'm just running the first few cups of RO down the drain, and I'll see how this impacts the slime algae.

Relatedly, what do you all think of long-term use of trash cans for RO storage? Do they leach?

[David Grigor]

What you are experiencing for the first cup or so after turning on is normal. Why I can't really say I'm sure in a FAQ type section of any of the filtration vendors can answer if you really want to know. Best to make large batches of water vs. very small batches of water for this reason and why having ro directly to your tank via a float valve is not advisable since it is always small increments ( not to mention other dangers why you wouldn't want to hook up your topoff directly ).

However, if you run a DI cartridge after the RO membrane, it should take care of that initial high tds output.

Your RO storage should be at least NSF rated plastic. Also, airborne can also make the TDS reading higher from your storage container so keep a lid on it.

[mrbill]

Normal, also if your RO storage didnt have a tight fitting top any evaporation would elevate the TDS.

[johnzillmer]

The storage container had a pretty tight lid; since it is in an old basement I didn't want any more humidity down there, nor did I want any of the nasty dust settling in.

It makes me feel better that this is normal. I still wonder, though, if something is up with my RO production/storage system. The slime algae problem is relatively recent and, more tellingly, is worse after a water change. I tried 10 gallons of RO water from another source, and did not get the slime. I intend to replace the trash can (with a glass aquarium), and run the first couple cups of RO down the drain, and see how it goes. I bought a new 75gpd membrane, but if I can save it, I would like to get more life out of the old membrane.

[David Grigor]

Always recommended to use DI after RO membrane so should consider getting it as an add on. A dual one from filterguys.biz runs about $50.

A slime coating ( not visable just by touch ) in the RO/DI storage container itself does occur over time. I typically wipe it out with bleach and let air dry a few times a year.

[johnzillmer]

Update: I've replaced the questionable trash can reservoir with a pair of aquariums -- a 20 for the RO water, and a 29 below it, into which I run some of the RO water and then mix it up to 1.025 with Instant Ocean. TDS meter is still showing minimal TDS (seems to vary between 1-4 depending on the day).

Problem: still experiencing slime and diatoms *after* 10% water changes in the reef. Also, I just set up a 10 gallon freshwater tank -- thread algae outbreak just like I've been fighting in a 2 1/2 gallon planted tank that I thought I just overdosed with iron. Huh. Still something in the water.

Since I live in Mpls, and they put phosphorus into the water (to control corrosion), could it be that enough PO4 is getting through, even with only a couple PPM of TDS? Anyway, I've installed a new membrane, and have a DI canister coming from The Filter Guys. See if that works...

[Redwinger]

You might want to try a silica buster DI resin as the diatoms are a result of silicates in the water. IMO the 1-4 tds is not your issue. Mine is usually around there with no algae problems what soever. My RO container is a rubber maid trash can with a open top and has been like this for 2-3 years.

[johnzillmer]

You might want to try a silica buster DI resin as the diatoms are a result of silicates in the water. IMO the 1-4 tds is not your issue. Mine is usually around there with no algae problems what soever. My RO container is a rubber maid trash can with a open top and has been like this for 2-3 years.

I thought a couple ppm TDS should be no problem as well. Do silicates get through the membrane easier than other minerals?

I have other odd algae issues as well -- slime in the reef, and the freshwater thread algae, that I mentioned I had previously attributed to heavy-handed iron supplementation. That, along with the fact that Mpls adds phosphorus to the water, made me think low levels of PO4.

[Redwinger]

Why would you be adding iron? You might want to run a dual DI at the end of the system to remove it all.

[johnzillmer]

The iron is (was) being added to a freshwater planted tank. The connection with the RO issue is that the planted tank gets water from the same source (the RO filter) that the reef tank does, and so I suspect now that the problems in the two tanks are related in that way.

A better question, I think, is 'Why, City of Minneapolis, do you add PO4 and so much chloramine I need 3-stage carbon filtration on my RO?'

[Redwinger]

The iron is (was) being added to a freshwater planted tank. The connection with the RO issue is that the planted tank gets water from the same source (the RO filter) that the reef tank does, and so I suspect now that the problems in the two tanks are related in that way.

A better question, I think, is 'Why, City of Minneapolis, do you add PO4 and so much chloramine I need 3-stage carbon filtration on my RO?'



Oh I see now.:smile:

[johnzillmer]

So I solved my problem -- the membrane was bad, even though it was only letting 1-4ppm TDS through. After installing a new Filmtek 75GPD, it is running at 1ppm consistently, and I am getting no slime or diatoms after water changes. I guess the typical 'as long as you are getting >95% rejection, you are ok' doesn't always work, since I was getting just over 95% rejection (90 ppm in, 4 ppm out = 95.6% rejection).

I just received (and hooked up) a DI canister from the Filter Guys, as another line of defence against the nasties in the municipal water.