Hydroponic PH down usage

[ALLISON DUHAIME]

We are currently sitting with a PH of around 7.6, which we understand needs to come down. We have had our goldfish dying every couple days and our plants are drying up and turning colours. We understand that our system is young and needs to sustain itself, but we feel it needs a little assistance or boost & a big drop in PH.

We have tried:

-2 bottles (over the course of the month) of PH down from our local petsmart - we didnt realize that it wasnt doing much to bring the ph down

-a water change - system didn't change, even though we add cooled down boiled water;

-diluted vinegar in a water addition with a ph level below 6 - water in the tank/system is reading between 7.4 & 7.6 after the water addition was made of 62 L (consisted of half tank water and half cooled down boiled water from a hot water tank) and 1 cup of vinegar that sat for 24 hrs and was added over the next 24 hrs 

We found this community and started researching and still searching the whole community, 

we found that ph down from a hydroponic store is better then that from a pet store/aquarium store; this prompted us to visit the hydroponic store and purchased a small bottle of 85% PH Down Phosphoric acid . We would like to find out a safe formula for adding this or if its even safe to use in our AP system?

[TCLynx]

I would recommend that before you turn your AP system into more of a chemistry experiment, you need to do some water tests.  Can you test for ammonia, nitrite and nitrate? as well as pH?  How are you testing your pH?

What is your media?  Are you sure your media isn't affecting your pH?

What is your source water like?  What is it like after it has bubbled overnight?

Why are the fish dieing?  Is it because the ammonia or nitrite are high?  or are they just cheap feeder goldfish that were meant as bigger fish food and not to survive long anyway?

A pH of 7.6 while a bit high and it would necessitate the need for chelated iron and perhaps give you issues with potassium lock out as well, will not cause all plants to dry up (though some turning colors is likely from potassium lock out, I've been dealing with a system with a pH of 7.6 and above for 4 years now.)

First, if your tap water or your media is causing your pH to be way high, then constantly using acid is not a great way to go to deal with your problem.  By using acid on calcium carbonate rich water, you are simply bringing the pH down which dissolves more of the calcium carbonate thereby releasing more calcium into the water which will cause more of the potassium to precipitate out of solution and it will just make some of the nutrient issues worse.  See the iron issue may simply be caused by high pH but the potassium issue is actually because of the overabundance of calcium in the water.  So, to deal with hard water you may need to collect rain water for top up or use an RO filter.  If your media has limestone, marble or shells in it, you will have to replace the media.