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To start I am fishless cycling my system which has a 75 gal aquarium, 28 gal sump and 50 gal Rubbermaid stock tank as a grow bed.

 

To combat a very high ammonia level of 8+ (the green was darker than the chart on my API kit) I added about 20-30 gallons of water to my system using a dechlorinization filter which topped off my system.  Prior to the top off my pH was at 6.8.  After the top off and cycling my system for over an hour (it floods and drains about 4-5 times an hour) my Ammonia was down to 6 and my pH was up to 7.0.  I was looking for and expecting a pH lift to help with the nitrification process and the water out of the tap generally runs between 7.4-7.6 pH.

 

Later I added 12 oz of MaxiCrop with Iron because I had been getting some yellowing and die-off on my lettuce and kale transplants.  I cam to the 12oz total based off of the 1 qt recommendation per 250 gallons that was in Silvia's book.

 

This morning my Ammonia is still at 6 but my pH has crashed down to 6.4.  My nitrites and nitrates have remained pretty constant at 5 and 80 respectively (I was able to jump start those with them filter water from a co-worker who raises Koi)

 

My question is: has anyone ever run into this before?  Initially I couldn't find anything that said MaxiCrop would affect pH but after doing some digging on Google, others in the Hydro world have had this issue although it is rare

 

I've added about 1 Cup of Reef Aquarium substrate "Aruba shell" in a bag to the grow bed under the inlet that my Dad had from when he was doing Saltwater tanks.  I know this will slowly help buffer the pH back up and I am considering other methods as well.  I intend to move slowly, but this just seemed like an odd problem to crop up

 

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As part of the nitrification process the bacteria will acidify the water (lower the PH) so that is a good sign. Your ammonia should ideally be at 4 but now you should just wait until it reaches zero. Then take the ammonia to 4ppm again and if it drops to zero with in a day or two you are probably ready for fish. Try not to over compensate to have drastic PH swings as that is bad for living things. The shell grit should be all you need to buffer your PH. If it gets lower than 6.0 then you may want add some potassium hydroxide or potassium carbonate

For what its worth, your lettuce and greens like a ph of about 5.5 (I'm also a hydro grower), but our fish don't like that...  All works pretty well between 6 and 6.5.  As jonathan pointed out, don't try to compensate while cycling...  Left to its own, your system will find its center.  Since I posted to your other post, I won't repeat that here but you might want to consider some of teh ecological labs products I use (on my home page).  I'm thinking Nourish L and Photosyntesis Plus.  Once your system is stable you might want to consider Nightout II on a monthly baisis--but I would not interject it until you're stable.

Your PH at 6.4 is where I try to keep mine. Below 6 and you will be in danger of harming your bacteria and above 7 your Iron will become locked and unavailable to your plants. I try to keep my 15,000 gal system around 6.4 ph

Jonathan and Robert have both given you good advice.

What are you using for grow media? I had the same problem when I started up, and it turned out that after trying to lower my PH, nothing was happening until one day it just crashed down to the lower sixes. It turned out that I had finally broke the Natural PH buffer from the water source I was using, which was municipal water from Lake Michigan. It runs about a PH of 7.2 to sometime 7.8. Municipalities often keep it higher so it doesn't damage the pipes in their system. Just adjust it back up slowly, and don't over do it. It may swing up and down a bit, but eventually, it'll settle in.

On a further note Suzanne, I read the back of my MaxiCrop w/iron liquid, and it stated something about acid loving plants. I am assuming that this could lower your PH. I used to spray this stuff on the leaves, but found it left brown spots that eventually ate through the leaves, so now I just spray around the base of the plants. I ordered some of the chileated iron to add to the water, as I don't need the extra ingredients in my year old system anymore. I would suggest adding some PH up in lower doses until you get to where it needs to be. GL.
 
Matt T. said:

What are you using for grow media? I had the same problem when I started up, and it turned out that after trying to lower my PH, nothing was happening until one day it just crashed down to the lower sixes. It turned out that I had finally broke the Natural PH buffer from the water source I was using, which was municipal water from Lake Michigan. It runs about a PH of 7.2 to sometime 7.8. Municipalities often keep it higher so it doesn't damage the pipes in their system. Just adjust it back up slowly, and don't over do it. It may swing up and down a bit, but eventually, it'll settle in.

I'm using expanded clay so that should be an issue.  I've started buffering with crushed shells and adding lye potassium bicarb as needed.  Everything seems to have stablized

Ammonia that high will inhibit cycling.. i'd try to get it under 4 with a couple of partial water changes

12oz of the maxicrop is a bit much, but it won't lower your ph.. i used 1 capful for each 55 gallon growbed, 1x every 3 or 4 weeks in the early stages of my system..

now, with a ph of around 7.4, in the 3 gb system (each gb is 1/2 of an IBC) i put maybe a cup of maxicrop with iron, every couple months

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