My tap water is in the high 8.4 ph area. Any "natural" ways to lower it?

[David W. Russell]

I just got my system running and found out that my tap water is high in ph.  Any natural ways to lower it before I add my fish??

[Robert Rowe]

I am sure glad we have some chemists on this forum

TCLynx said:

Here are some blog posts about pH and tap water that might help enlighten.

ph and tap water

pH and Tap water2

To lower pH, you need to use acid or remove the hardness (Remove, carbonates and bicarbonates and alkalinity) somehow.  How much acid is needed is going to be more related to the amount of hardness in the water rather than the actual pH of the water so it can be really tricky to figure out how much acid to use simply based on your starting pH and what some one else does somewhere else.  They may have far more hardness they are counteracting than you do so if you add the same amount of acid you may overshoot.

Since you say the system is brand spanking new, you could probably go ahead and do some acid adjustment right in the system since you don't yet have anything to kill.  However, as soon as you start growing your bacteria, plants or add fish, you should do pH adjustments to top up water in a separate tank and aerate it and let it settle before you add it to your system.

Drawback with Lemon (citric acid) is that it has antibacterial qualities that can cause problems cycling up a new system.  Vinegar doesn't seem to have as long lasting effects (it breaks down) so you need quite a lot of it to counteract the carbonates.

Muratic acid tends to be long lasting and effective but keep in mind that the chemistry will break up things like calcium carbonate, the carbonates will get used up counteracting the acid and the remaining calcium and chloride will combine to form calcium chloride which is a salt.  (If you are constantly needing to use lots of acid all the time to keep your pH down, you may find issues with higher TDS and some things like strawberries might not like it.)  Collect rain water or use some RO water so you are not constantly having to use acid.

You do want some minimal amount of hardness in your system water since it will help buffer and keep the pH from getting too unstable and crashing too low.

I have used phosphoric acid but be careful when using phosphoric acid in a system near the time you also dose chelated iron or you might cause a bit of a snail die off (which might cause you to need to clean snails out/off your pump to keep from clogging it and restricting flow.

[Linda Logan]

I have a very small pond in which there was one goldfish that over wintered and several water plants just barely starting to grow again and lots of frog eggs and polywogs.  I took the goldfish out and tested the pH expecting it to be in the 6's as it is always topped up with rain water.  I tested 3 times - it was 8.4.  Now two weeks later I tested kH and gH based on TC's post.  It showed minimal kH and some gH and the pH was 6.4.  The main difference is that the pond plants have put on considerable growth.  I'm guessing that this has altered my pH.  I never tested ammonia or nitrates etc.

My point is that plants growing will naturally bring pH down.  So maybe minimal intervention is needed on the high pH tap water.

[Linda Logan]

My last remark sounded off after I pressed send.  Apologies if I came off badly.  Mainly found the change in the pond in such a short time interesting.

[TCLynx]

pH can swing quite wide due to several possible things.  Algae can cause a daily pH swing, if you pH is low at dawn and high late in the afternoon, it could be due to algae giving off dissolved carbon dioxide during the dark hours and using up dissolved carbon dioxide during the daylight hours, (FYI if you have an algae bloom you need to add extra aeration especially for overnight since when algae is giving off the CO2, it is also using up dissolved oxygen.)

Anaerobic pockets can also cause pH to rise (no I don't think this would happen in the brand new system of the original poster, they are probably just dealing with hard tap water to begin with.)  A pond that has been shut down and overwintered might have a high pH initially since there could be some stagnant pockets from being shut down and once things get flowing and aerated again the pH will come back into it's more normal range. 

The nitrification cycle will naturally bring pH down and this is why you so often her about people needing to add a "buffer" to buffer the pH back up regularly.  Now some people will claim they never do that but if they are adding tap water or well water, it is likely coming with some natural buffers already in it (calcium carbonate or hardness.)

One of the best ways I can think of to balance hard tap water is to collect and use as much rain water as you can if you happen to be in a climate suitable to do that.