Delayed rise in pH after mixing RO and tap

[jmueller]

Hello,
I am in the process of setting up a 75 gallon tank. Where I now live, the water is very hard. The RO had a pH of about 6.2 and the GH and KH was very low. Trying to get some substance back to the water and to buffer the pH some, I mixed water 9/1. My tap water has a pH of about 7.6 and the GH is around 300 mg/l. I put the mixture in a glass jar and shook it up well. The pH went up to about 6.8 and the GH and KH both measure in the 40-50 mg/l range. I thought this looks ok.

I filled adding 7.5 gallons of tap water to get the numbers mentioned. I let the filter run a bit and rechecked. The numbers were the same. 2 days later, the pH has jumped to 7.5. What's going on, and how do I get that pH back down below 7?

Thanks in advance!

Jon

[alron2]

Is the tank bare Bottom? Any rocks in the tank? What is the background?
Ron

[jmueller]

Hi Ron,
The tank has no substrate and there are no decorations in the tank. The filter (canister) has carbon and ceramic rings. That's it. I'm wondering if after some time, the pH of the water came up because of the tap water. I don't know if that happens though.
Jon

[alron2]

Jon,
Test your tap water by letting it sit overnight with air stone and a heater. If the ph comes up it is because of the Co2 leaving the tap water. The solution is to age your tap water before mixing to the desired ph.
Ron

[Neptune]

Not unusual for the tap water pH to rise after sitting for a time. As alron2 says its the CO2 off gassing.

[jmueller]

Thanks! I am running some samples overnight with air stones & heat. Will be interesting to see what I get - tap, RO, 10% tap, 5% tap. Is 5 or 10% tap enough, or should I add a chemical for buffering & minerals?

[alron2]

I believe you should run one test with 100% tap so we can make sure it is the CO2 causing the problem not some with your RO water. I have learned to never assume anything in this hobby, test and retest, especially if it is cheap to do.
Ron

[jmueller]

The RO went from 6.1 to 7.2. The 5% went from 6.4 to 7.5. The 10% went from about 6.6 to 7.6. Does this make sense?
I am testing the tap now. Does this make sense? IS it typical for pH to go up by ~1 when CO2 is released?

[jmueller]

The RO went from 6.1 to 7.2. The 5% went from 6.4 to 7.5. The 10% went from about 6.6 to 7.6. Does this make sense?
I am testing the tap now. Does this make sense? IS it typical for pH to go up by ~1 when CO2 is released?

[DJW]

What you are seeing is not that unusual. My well water is a little extreme, it has a lot of CO2 so it comes out at pH 7.1 and with aging/aeration goes up to 8.6. The RO still has CO2 in it... it starts at 5.0 and goes up to 6.4 as it ages.

Your tap water looks like the dKH (carbonate hardness) is high, maybe around 15. Have you measured the KH? It is the KH that determines the pH of aged water.

The idea that you need a pH less than 7 is a leftover from the old days of the hobby, when all you could get was wild discus. If you want to have a low pH you will have to use almost pure RO and keep an eye on the pH as it will have a tendency to fall.

Your RO filter isn't working quite as well as it could. Maybe the pressure is low.

[jmueller]

Thanks, Dan. My tap water is >300 mg/l KH. My RO unit is bringing this to ~20 mg/l. When I tested the 10% tap mix, it as ~40 mg/l. My pressure in the house is set to 65 PSI, but, I notices the flow rate went way down when I installed an iron curtain, several years ago.

I tried discuss when I was a kid, and failed. Now 30 years later, my son and I are taking a crack it and I am trying to get the water dialed in. Your comment about pH less than 7 is good to hear. I've been targeting <7, but I'm not sure I can get there anyway with out using a LFS chemical. Using mixes makes me nervous, and that's why I was trying to come up with a good RO/tap mix.

I have nothing in the tank and am wondering if a large piece of drift wood would help. I've read that can help bring pH down, but am imagining that's a short-term thing???

Jon

[DJW]

As much water as you need to change to keep discus healthy, the driftwood won't have a chance to make much difference.

I think what I would do is start with a mix that results in KH of 40-50mg/l. That provides enough buffer to keep the pH stable between WCs, and if the pH is 7.6 then that's okay. You can always make adjustments and see how the fish are doing. Filip, who is a moderator here, has water a lot like yours. I don't know if he uses RO, but you can check with him and maybe he can recommend a good mix.

Discus don't do well with a lot of bacteria in the water, and the best way to control bacteria is with frequent water changes. The main benefit of low pH in the native water is low numbers of bacteria, but its a lot of work to keep a tank at a low enough pH to inhibit bacteria to a significant extent.

IMO using chemicals to push the pH down is ill-advised and comes from a misguided preoccupation with having a certain pH.

[Filip]

Hi JMueller and welcome back to discus again .
A lot has changed about keeping discus since you were a kid and particularly the belief that soft and acidic water is a must with discus .
Like Dan said , I live in a town with a very hard water parameters ideal for Malawi Chiclids , and yet there are many succesfull , straight tap , discus keepers here .
My tap PH starts with 7.2-7.5 range and stabilize on 8.0 after a one day age after the co2 gasses off .
KH -16-17( around 250 ppm ) and TDS 330 ppm .
8.0 PH is the high end IMO for discus keeping but still doable , so just ageing your water will be enough for a proper care , but 20-30 % RO won't hurt either .

The bottom line is that fresh and bacteriologically sterile water is what's most important for discus health .Almost anything else in water and in tank can be adjusted to our needs , except the discus need for clean and fresh water .

[jmueller]

Thanks all for the inputs! I really appreciate it. Another question - what do people typically use for storing their water? I get nervous about plastic garbage bins - do they outgas or leach chemicals into the water? I've read comments about "food safe" garbage bins, but I don't see that on labels in the stores. Any thoughts?

Thanks,
Jon

[Ryan925]

Thanks all for the inputs! I really appreciate it. Another question - what do people typically use for storing their water? I get nervous about plastic garbage bins - do they outgas or leach chemicals into the water? I've read comments about "food safe" garbage bins, but I don't see that on labels in the stores. Any thoughts?

Thanks,
Jon

I don't age but what from what I see here brute cans are the go-to