Help with Remineralizing RO Water and Keeping Acidic pH?

Hello all,

I am setting up a tank in which I hope to breed German Blue Rams. I live in Texas, and my tap water is hard with about 10 dGH and 6 dKH, as well as a pH of ~8. So, I will be using an RO/DI unit to fill this tank. I am looking for a remineralization method that would restore the RO water's GH and KH to an ideal level, while not raising my pH, since I am looking for an acidic pH of around 6.5. My pH meter doesn't work for RO water according to the instructions, but it is my understanding that RO water tends to be around pH of 7? Anyways, I need a method to be able to keep my tank at a stable and slightly acidic pH using remineralized RO water.

Thanks!

 

I am looking for a remineralization method that would restore the RO water's GH and KH to an ideal level

Ideal level for Mikrogeophagus ramirezi is GH 0, KH 0, pH 5-6. Instead of buffering via KH you just use humic substances (aka "tannins"), ideally extracted by yourself from alder cones or using IALs and oak leaves directly in the tank. I'd do both.

You also don't look to get the right pH in softwater tanks*, you look for the right TDS (total dissolved solids) and/or EC (electric conductivity). Here you will want to have 20-60 mg/l TDS, equalling an EC of 40-120µSI/cm. A TDS-meter is mandatory for this kind of tank.

* Because pH-meters don't work under an EC of 100 and drip tests are not reliable below a KH of 2.

 

You don't need the DI filter for fresh water fish. MacZ has it right, it's the TDS that matters. You can use the RO (without DI) and remineralize with your tap water until your TDS is right. IME a TDS of 90 is fine.

 

It's not even necessary to remineralize at all. Especially for M. ramirezi. With humic substances, DOC and other dissolved solids from wood, rocks and even "inert" sand, a TDS level of about 50-70 should dial in by itself. Completely sufficient and at those levels the chance of bacteria on the eggs is virtually zero.

 

You don't need the DI filter for fresh water fish. MacZ has it right, it's the TDS that matters. You can use the RO (without DI) and remineralize with your tap water until your TDS is right. IME a TDS of 90 is fine.

Interesting. What does the DI even do? I am fairly new to these concepts and the DI just came with the RO unit.

It's not even necessary to remineralize at all. Especially for M. ramirezi. With humic substances, DOC and other dissolved solids from wood, rocks and even "inert" sand, a TDS level of about 50-70 should dial in by itself. Completely sufficient and at those levels the chance of bacteria on the eggs is virtually zero.

I had heard that using straight RO water was not ideal for fish as they need some of the minerals, and pH can be prone to heavy crashes. I also want to keep a pair of angelfish in this tank. Would those also do very well in these parameters?

 

I had heard that using straight RO water was not ideal for fish as they need some of the minerals

Softwater fish are adapted to these conditions. BUT it is necessary to acclimate fish slowly when moving to a tank with vastly different readings.
Look up the numbers from the wild. You will see many readings from South America are equally soft to distilled water.
Water values South America (Map pH) - Südamerikafans
Water values South America (Map Conductivity) - Südamerikafans
The humic substances also help the fish take up and retain the minerals they need from their food.
That said: Make sure they get a highly variable diet of frozen and life foods. Don't try this only feeding dry foods.

and pH can be prone to heavy crashes.

That's a misconception. Assuming one only uses the carbonate buffer system (measured with KH) this is possible, but in softwater aquatics you use humic substances as an alternative. The stuff buffers between 4 and 6 and believe me: It's unbelievably stable especially when not only adding the humic stuff, but also botanicals and leaf litter.

I also want to keep a pair of angelfish in this tank. Would those also do very well in these parameters?

Should work, too. Again, acclimation is key. Once the fish are acclimated you will notice they do better in soft water than tap.

What does the DI even do? I am fairly new to these concepts and the DI just came with the RO unit.

DI removes the few Ions the RO membrane leaves in. The difference is marginal and DI is basically only useful if your tap has significant salt content.

 

BUT it is necessary to acclimate fish slowly when moving to a tank with vastly different readings.

Thanks, you seem to be very experienced. How should I go about acclimating, and how long would this typically take?

 

Drip acclimation. Set it up for 2-3 hours. Until you have diluted the transport water 2:1 or better 3:1 (RO:T).
I have to do this each time I get fish as I have readings of 35-40 mg/l TDS and an estimated pH of 5 or just below that. Luckily I only buy fish maybe once a year.

 

Rams originate from water that varies a lot seasonally, so while they do great in very soft water, it isn’t absolutely necessary. Anything below 200ppm is probably fine, but the suggested 50-100 is a safe range. If you want to remineralize without increasing pH, then add salts that only increase GH (not KH). There are a lot of these mixes available for either fish or shrimp tanks.

The difference is marginal and DI is basically only useful if your tap has significant salt content.

DI is needed if you want the TDS to be as close to zero as possible. Which is needed for saltwater or extreme blackwater.

My pH meter doesn't work for RO water according to the instructions, but it is my understanding that RO water tends to be around pH of 7?

If you add NaCl to the water, you can measure it’s pH. The pH of RO water usually settles around 5.5 due to the dissolved CO2.

 

I have to do this each time I get fish as I have readings of 35-40 mg/l TDS and an estimated pH of 5 or just below that. Luckily I only buy fish maybe once a year.

Alright, thanks. On another note, how do you go about water changes in your soft water tanks since they have such a low pH? I would imagine just putting in some 7.0 water from the RO unit would be a shock to the fish if they are used to sub-5.0. How do you work around this, or does it not actually matter? Do you treat your new water with something to lower the pH before you add it? I am intrigued by your methods as softwater stuff is all quite new to me...

 

The pH of RO water usually settles around 5.5 due to the dissolved CO2.

 

DI is needed if you want the TDS to be as close to zero as possible. Which is needed for saltwater or extreme blackwater.

Depends, really. My thought is: If a good RO unit gives out permeate with a TDS reading of 5mg/l, an additional DI, bringing it down to 0-2mg/l is not a big difference.

How do you work around this, or does it not actually matter?

It doesn't really matter. Basically simulates a heavy rainfall. And as Ben wrote: RO settles in the 5-range, not 7.

Do you treat your new water with something to lower the pH before you add it?

Nothing for the pH. But as RO is usually pretty cold when it comes from the unit it stays comparatively cold in the canisters, usually around 16-18°C. So I add RO from an electtric kettle to bring it up to temp for the tank. I see that as much more important than pH.
I also add humic substances in the form of alder cone extract, but not necessarily to the bucket before adding to the tank.
In any case: I see my fish surfing the current of the freshwater inflow and looking for edible particles stirred up by it, so it obviously is not a problem.

 

Depends, really. My thought is: If a good RO unit gives out permeate with a TDS reading of 5mg/l, an additional DI, bringing it down to 0-2mg/l is not a big difference.

That’s probably right. In my case, my RO water is about 3ppm before the DI stage, zero after. But, if that 3ppm is chloramine, I can remove it without adding sodium thiosulfate, which adds a “lot” of TDS, by blackwater standards. And the DI cartridge lasts a long time if I use a bypass valve to bleed out the TDS creep.

Probably a little more granular than the OP needs, but that’s why I use it.

 

That’s probably right. In my case, my RO water is about 3ppm before the DI stage, zero after. But, if that 3ppm is chloramine, I can remove it without adding sodium thiosulfate, which adds a “lot” of TDS, by blackwater standards. And the DI cartridge lasts a long time if I use a bypass valve to bleed out the TDS creep.

Probably a little more granular than the OP needs, but that’s why I use it.

I always forget you live in a country with chlorinated tap. Things I don't have to worry about.

Though still, a good unit should remove chloramines in the active carbon stage. It's the smaller ions like chlorine itself, Na(Cl), K(Cl), Iron, Copper... which slips through the membrane, that stuff that I would aim at with the DI.

So, put in perspective: There are uses for a DI-stage and whether it's a must-have depends on circumstances.

 

The activated carbon stage breaks down the chloramine into chloride, ammonia, and nitrogen gas. Both the ammonia and some chloride make it to the RO membrane and the DI resin, and a very small amount gets past that. Do you absolutely need the DI? For marine inverts, probably yes. For freshwater fish? The LD50 is high enough that the RO likely suffices. But, the DI will compensate for some degradation in the prior stages, which becomes meaningful over time. So it makes the overall system slightly more robust.

People who don’t need 0 TDS water can absolutely just use RO and then add Prime.