RO Filter Size Question

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Pinkey

Pinkey

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Nov 16, 2004
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Nate
I have an open-topped 250 gallon setup (two 125g tanks plumbed together). I keep south American cichlids in one tank and assorted community fish in the other tank. Both are planted. I add 2.5-3 gallons of water per day to replace what has evaporated. I live in an area with really hard water. The short version; I need a water filter. I have access to a water pipe and will run 1/4" tubing from that to an auto top off system. Space is not an issue.

What filter makes most sense?
Filters seem to be rated by time and gallons which seems confusing to me. If a system is rated to purify 50 gallons per day and is rated for six months, does that mean 50 gallons X 180 days = 9,000 gallons? If so, does that mean that same burly system would last me 3,000 days?

Unnecessary Background: read if interested
I was testing my aquarium water this morning and smugly thinking about how all my ammonia, nitrite, and nitrates are unreadably low. My pH, because of the hard water, has never been anything other than 7.6. My plants do most of my filtration. I have not done a water change in 3 months.

The test strips showed me the hardness is at the highest possible reading which means it's KH of 240+ and GH of 180+. The + is what made me realize I've been adding buckets of minerals for months. This can't be good. I'll start a water change routine today.
 
T

TwoTankAmin

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Apr 2, 2002
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You need to drop these numbers gradually. I mean over several weeks. I don't usually see KH being much higher than GH (I assume the numbers are ppm). I am surprised that your pH is not higher.

I have had an RO/Di unit for a number of years. The filter lasts as long as it does depending on how much stuff that has to be removed and then how much water you pass through it. Forget the rating, you will know the components need replacing when the TDS of the output water begins to rise. So you will at least need a digital TDS tester. I have used this one for years. I only need 11-12 gallons of RO/DI a week for a 55 gal. tank and I have a portable 75 gpd unit. It actually outputs more like 50 gpd but I do not use an input pump. I run water to fill about 45 gals, worth of containers every 4 weeks or so.



You should be able to find it on sale somewhere for $12-$15

But I am not sure what your plan is here. I am assuming you want to do water changes and that you want to mix RO water with tap water? I am not sure of the goal but, if you lower the hardness and KH, you will also drop the pH some most likely. Fish can handle pH changes much better than changes in TDS.

TDS is a measure of everything dissolved in one's water. This mean things under two microns in diameter. It does not tell you what those things are, only to what they add up. It sounds to me like the plants have been keeping things from coning apart.
 
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Pinkey

Pinkey

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Nov 16, 2004
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Denver
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Nate
Thank you for taking the time to explain this. It makes sense in hindsight to simply test the water coming from the unit. I'm also glad you warned me about fast changes. I probably would have done a water change and filled the things up using my fancy new water. The longer term goal now is to soften over a couple of months. Once the readings start moving I supposed I'd have to calculate the bottom based on who I'd like to live in my tanks. Discus have always been off the table because of my water. Reasonably soft water opens a lot of doors for me. I hadn't thought about it being too soft yet.

Compared to the rating, you barely use your RO/Di unit. Does that mean the filters last you for many years?
 
T

TwoTankAmin

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Apr 2, 2002
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New York
I have been making ro/di water for about 10 years. In the winter I make it for my brother to put into humidifiers. He can burn through 2-3 gallons a day. So when I batch I run about 75 gals. He stores 29 and I store about 45. I changed the charcoal and RO membrane once and then I had my bro buy his own unit. I batch alternately between the two. He uses twice as much as I do when he uses it. But he uses if for less than half the months of the year.

The units we use are portable. When I do weekend fish events where I sell my offspring I bring a bunch of my RO/Di water to get tanks set up Then I have all the Python faucet adapters so I can run my unit in my hotel room. I just batch water 50/50.
https://store.afwfilters.com/revers...e-aquarium-ro-di-system-with-75-gpd-membrane/

You may want to poke around that site. They do it all.
 
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fishorama

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I just want to reinforce TTA's take on TDS. It sounds more complex that it really is. TDS means total dissolved solids, minerals & organics (all!). I feel a bit lost since my TDS meter died but I haven't replaced it yet. It's a helpful tool to understand your particular water conditions & we all have different water & even seasonal water. I don't test often but it can change...You need to know when that is likely to happen. Spring melt? Summer drought? Fall rains?
 
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fishorama

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Jun 28, 2006
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SF Bay area, CA
What a cheap but interesting way to measure different stuff in our tanks. I'm putting it on my next Amazon list. Nothing like a quick & easy test. The 1 I had did temp too in either C or F, no big deal, we all can google if we can't do the math...anymore, lol
 
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