r/o plumbing questions

Hello everyone,
I hooked up my R/O unit in different configurations today and would like to share the results,
1. Serial connection (waste water output of one membrane into feed of the second membrane)
46 gpd output, Tds=14ppm, ph=6.1 & moderate waste water
2. Merlin type connection (waste water output of one membrane into feed of both membranes)
64 gpd output, Tds=45ppm, ph=5.3 & very little waste water.
3. Parallel connection
very little output and a lot of waste water. So I didn't bother testing the output. (I'm guessing that the input pressure drops too much because of the split into to feed lines and reject increases like crazy)

Tap water comes out @ Tds = 325ppm , ph = 8.2

I have no pumps or waste water flow limiters.

I need to lower the Tds without sacrificing the product water quantity.
Any suggestions? (pumps, limiters, other configurations etc)

Best wishes to all..

Unless you're breeding then your water seems just fine for discus. My TDS is well over 400. But, if you do need RO then the way to double up the membrane is to split the source water, and not re-filter the waste water. I did this some time ago and doubled the production while keeping waste water around the same by using a ball valve in place of a flow restrictor, but I use my waste water for grow outs and adults.

What is the GPD rating of your filter (not what you are actually producing)?

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Originally Posted by jeep

Unless you're breeding then your water seems just fine for discus. My TDS is well over 400. But, if you do need RO then the way to double up the membrane is to split the source water, and not re-filter the waste water. I did this some time ago and doubled the production while keeping waste water around the same by using a ball valve in place of a flow restrictor, but I use my waste water for grow outs and adults.

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Thanks Brian,
I forgot to mention , I'm trying to breed. The ball valve idea is pretty cool , though. Thanks for that.

If your unit is producing 46gpd the we can assume it's either a low production unit or you have low water pressure. Most RO filter components are the same, so if it's a 50gpd unit then you can probably buy a 100gpd membrane and double production that way. If it's due to low water pressure you can buy a booster pump.

I believe in theory, water pressure would decrease in the serial set up from one unit to the next, but the water pressure to each unit would be the same in a parallel setup. I ran mine that way for years to get more output. I bet you have low pressure in general.

I have one 50gpd membrane, and the new one is 75gpd. (I'll switch the 50 later, I had it in hand, and bought the 75 later)
I have 325ppm tds out of the tap, kh=7, gh=11, and Calcium is 60ppm .
I haven't measured the R/O water yet for kh, gh and Ca.
But my tap/Ro mix gives kh=3 @tds=100, and kh=5.5@tds=150.
My two pairs ate their eggs @ 48th hour with only 5-10 calcified eggs @80-120ppm tds. after fanning them non-stop all the time. One of them is a platinum albino, and the other a red passion pair.

Increase your percentage of RO to waste. Target 70-80ppm...