Ro/DI water ph is 9.5!!!

Recently I have noticed that my ph in my tank has been rising. Before itw as around 8.0 ~ 8.2 but today it is at 8.5. I checked the ph of my ro/di and it was 9.5!! Is this a big problem?

Also, I have been having massive algae and diatom outbreak. I clean the glass and 20 minutes later, another film of algae builds on it. My tang is having a time of his/her life but I am getting a bit worried. I just installed my new halides so could this be the problem?

 

I'm far from an expert, but it is my understanding that RO + DI = pure H2O which has a pH of 7 (it is only the impurities that cause pH to swing up or down). I would check your tap source water pH because if it's coming out 9+ from RO/DI then I'd wonder what it is at the tap. If it is lower than post RO then there is a serious problem with your RO, first step I'd take is to swap in new filters and new DI resin, beyond that I'm just not sure. Oh maybe check the TDS as well, it could be exhausted DI or even an expired membrane giving the issues.

 

The pH of RO/DI is not easily measured and means nothing. There are too few ions to measure so is not accurate. It is basically neutral and will quickly take on the characteristics of whatever you add it to such as top off or new salt and will not effect the pH of either of those to any extent.

 

well I picked up my rodi new from BWM around 3~4 months ago. It could be the di resin. I checked the TDS and it was at 003
When I add the rodi water to my tank during top offs, I get a massive spike in PH but then goes away after a few hours.

Today, The ph was at around 8.2 ~ 8.3

 

Certain DI resins can and do have an effect on pH so its best to stick with a trusted source and blend of mixed bed resins, too much cation or anion in the mix and it can affect pH. Its not a 50/50 blend.
With a TDS of 3 you are past due for a DI replacement, I change mine at anything other than 0 TDS on a consistent basis.