Post RO: 37, Post DI: 17...Does this DI filter look spent? (pic)

[gummyworms]

Hello,

I've been fighting some nasty hair algae in my tank, and I think I may have spotted the problem. Below is my first thread.

http://www.reefcentral.com/forums/sh...readid=1430298

I checked my RO and DI outputs today and found them to be:

Post RO: 37
Post DI: 17

Could this be the source of my algae problem?

I do not know the source TDS of my water because I the TDS meter is built into my RO/DI unit. I have owned the unit for about a year and have not replaced any cartridges yet. This is the unit I own:




And here is a picture I took today:



From this, it looks like my DI cartridge is spent (blue to gold color change), so I will be reordering that. Should I reorder the carbon block and sediment filters as well?

Thanks!
Shawn

[Buckeye Hydro]

A good rule of thumb is to replace your sediment filter and carbon block after six months. A more precise way to maximize the useable life of these two filters is to use a pressure gauge to identify when pressure reaching the membrane starts to decline. This is your indication one or both of the filters is beginning to clog.

Also be cognizant of the chlorine capacity of the carbon block. The Matrikx+1 (“Chlorine Guzzler�) for example will remove 99% of chlorine from 20,000 gallons of tap water presented at 1 gpm. Original equipment suppliers commonly provide carbon cartridges rated at 2,000 to 6,000 gallons.

Regarding your RO membrane and DI resin, use your TDS meter to measure, record, and track the TDS (expressed in parts per million) in three places:
1. Tap water
2. After the RO but before the DI
3. After the DI.

The TDS in your tap water will likely range from about 50 ppm to upwards of 1000 parts per million (ppm). Common readings are 100 to 400 ppm. So for sake of discussion, let's say your tap water reads 400 ppm. That means that for every million parts of water, you have 400 parts of dissolved solids. How do we go about getting that TDS reading down to somewhere near zero?

If you do some experimenting with your TDS meter, you'll note that your sediment filter and carbon block filter (collectively called prefilters) do very little to remove dissolved solids. So with your tap water at 400 ppm, you can measure the water at the “in� port on your RO housing and you'll see its still approximately 400 ppm.

The RO membrane is really the workhorse of the system. It removes most of the TDS, some membranes to a greater extent than others. For instance, 100 gpd Filmtec membranes have a rejection rate of 90% (i.e., they reject 90% of the dissolved solids in feed water). So the purified water coming from your 100 gpd membrane would be about 40 ppm (a 90% reduction). Filmtec 75 gpd (and below) membranes produce less purified water (aka “permeate�), but have a higher rejection rate (96 to 98%). The life span of a RO membrane is dependant upon how much water you run through it, and how dirty the water is. Membranes can function well for a year, two years, or more. To test the membrane, measure the total dissolved solids (TDS) in the water coming in to the membrane, and in the purified water (permeate) produced by the membrane. Compare that to the membrane’s advertised rejection rate, and to the same reading you recorded when the membrane was new. Membranes also commonly produce less water as their function declines.

After the RO membrane, water will flow to your DI housing. DI resin in good condition will reduce the 40 ppm water down to 0 or 1 ppm. When the DI output starts creeping up from 0 or 1 ppm to 3 ppm, 5 ppm, and higher, you know that your resin needs to be replaced. Sometimes people complain that their DI resin didn't last very long. Often the culprit is a malfunctioning RO membrane sending the DI resin “dirty� water. This will exhaust the resin quicker then would otherwise have been the case. Sometimes the problem is poor quality resin – remember that all resins are not created equal!

Russ

[gummyworms]

Thank you for the very thorough response!

So if I understand correctly... Since my RO unit has a 75 Filmtec, and it currently is outputting at 37, that means my starting water is likely around 1233 TDS, which is exceptionally high! I"m in the country on well water, and it is very hard. Does this usually translate to higher TDS water? I will have to verify this by purchasing an TDS meter.

I will definitely purchase a new DI, and grab some new filters as well. If my algae is being caused by poor quality RO/DI, is an output of 19 sufficient to trigger such a large problem?

[Buckeye Hydro]

Your math is spot on. I doubt your tds is that high. More than likely it is a lot lower than that, and you are getting a rejection rate lower than ideal.

Checking the tds of the tap water and calculating your rejection rate is a good place to start.

Most folks change their DI when the DI water tds level climbs higher than 2 or 3 ppm - so yes - you are way past due for a resin change out.

Russ