Gravel washing

[Michelle Silva]

Well, after I filled the second half of pots with the expanded shale and coco ocir (the other half is with chunky perlite and coco coir) I just read a post that reminded me that I didn't wash any of it!! How important is this??

[Michelle Silva]

It was actually was 6.5 - 8, not 6 as I stated before. I'm not planning to add anything just yet. It's approx 4500 gallon system and the high PH was in the one fish tank that has a higher concentration of fish that were just added yesterday.. I figure once that water all gets cirulated thru the remaining three IBC totes and the rest it will balance out. The two long raft tanks have 7.0 PH and the middle one had 6.5 at the end right before going back to fish tank.. I'm just leaving it alone for now. I am planning to get a lot of strawberries..so hopefully won't be a problem.

[Nate Storey]

Michelle, what TC said. I will say that I've gone over to running all of my systems with no in-system buffer material...I used limestone for a while, but now I like liming a lot better. I just depends on what you want to do. If you use coir, it will bring the pH down some, not as much as peat though I don't think. You might just have really heavy nitrification going on in some areas, but it might be worth it to add a carbonate buffer in the area where it's running 6.5, or you could let it go and see what it does. . . The maximum difference from one point in a system to another is a range of 0.20, with the average being closer to .04. The water coming out of my towers always has a lower pH (good sign of nitrification. . .)

[TCLynx]

Most plants actually like the lower pH better. However, the bio-filter can crash if the pH drops too low which would in turn lead to ammonia spikes and lack of nitrates and dead fish and nasty smells. So, if you are going to run a lower pH system, I would advise very close monitoring of water quality, pH and ammonia levels especially.

Higher pH the plants can sometimes have trouble taking on Iron and some other nutrients. A system with a higher pH is likely to also run higher nitrates since the plants are not as efficient at using the nutrients.

What is the best pH and how to keep it there, well that will vary depending on the system, media, source water, type of plants, type of fish and on and on. I've got my big system running at a fairly constant pH of 7.6 because about 40% of the media in the system is shells (Big top ups from the well or leaving the sump uncovered to cause an algae bloom can make it go up to 8 or more and heavy feeding along with lots of rain and dosing with Iron has seen the big system pH as low as 7.2.) Cucumbers and strawberries don't like that system.

My newer 300 gallon system is still a bit new for me to make too many statements about what grows and what doesn't but that system has only the brown river rock media and I've been having to add lime and shell grit regularly to keep the pH from dropping too low and crashing the bio-filter. I've already a couple times experienced renewed ammonia spikes because I let the pH drop too much.

It isn't that a system can't run at a low pH, but you really need to keep the pH steady if running at a lower pH since fluctuations tend to upset the bio-filter more the lower the pH is. It is also harder to steadily buffer at a lower pH. See Shells naturally buffer to 7.6 if the pH is above that, the shells don't dissolve and therefor don't raise the pH above that. Limestone and marble may buffer higher to like 8 or so. So far I've not discovered any material that will steadily (self regulating) buffer to a lower level so when you add buffer to a system that you are trying to keep at say 6.8 it is more of a challenge since if you add too much, you could bring the pH up higher than you intend and if you don't add enough regularly, the pH may drop lower than you like. How much buffer is needed per week or per day will depend on many factors so I don't know a formula that will say you need x amount of lime per y amount or water or fish.

The shells from the driveway might work. I would suggest that you run some tests by say putting some in a glass of distilled water and run pH tests on it for a period of time. See some shells will buffer to 7.6 but there are some corals and other shells that may buffer higher. You might want to know how self regulating your shells will be before just dumping them in. Again, you will probably need to try something and test to see how effective and how much you will need to make things stable. Minimal changes and test, if you go changing too many things at once, you won't know what worked and what didn't.

[Michelle Silva]

ok,what kind of shell grit? I have a shell driveway, could use some of that, as that is more readily available then oyester shells. What happens to the plants with the lower ph?

[TCLynx]

Wow that is quite a range of pH. I would definitely get some shell grit or lime to have on hand cause if you start seeing the pH too much below 6.5 you will probably want to buffer. Also, the coir may tend to bring the pH down the same way peat does (I've heard of some coir really bringing pH down and other stuff that stays fairly neutral so that varies.)

I just added a bag of limestone chicken grit to my 300 gallon system. I got a mesh bag and zip tied it such that the water going back into the fish tank flows through the small pebbles. Hopefully this will be a steady long term way to keep that system buffered so I don't need to worry so much when I'm away for a week. I like having the pH down below 7 because the plants take up the nitrates better but if the pH gets down to 6 on me I start getting spikes.

[Michelle Silva]

BTW,thanks for your reminder about PH testing.. I did test the PH today and depending on where in the system it ranged from 6-8. It was 8 where I added most of the fish yesterday at the highest fish tank (some of them are HUGE) and around 6.5 at the last place in the raft tanks before it goes back to the fish tanks.

[Michelle Silva]

I have quite a bit of the shale in the many of the ground pots which are 14" high,and 24" x 18". I did rinse most of the oir due to the issues I read about salt content..some of the coir that didn't get rinsed as much did some through the verticals quite brownish orange. There's no tanks over but it will recirculate back to the system via the liner underneath. I didn't handle the extra chunky perlite wet, although I did know about that..I'm glad that's in already, didn't like that stuff too much. I haven't started watering the ones with the shale yet..oh well, not going to worry about it now. Thanks for your reply. It was your post that reminded me!!

[TCLynx]

Well most gravel washing comments has to do with media based aquaponics and the fact that most gravel has quite a bit of sand, silt, clay or dust in it that would otherwise settle elsewhere in the system if it were not washed out first. Some times the "dirt" that is mixed in with gravel can have a profound effect on system pH as well. I have seen pictures of why one should wash their gravel first that basically showed a sump tank with 4" of clay settled in it when the builders thought they didn't need to wash their gravel.

But as you are dealing with far less media it might not be as big a deal.

However, the media you are dealing with is of a far different nature than gravel. Perlite should always be handled wet as the dust is really bad for the lungs. Coir varies greatly from stuff that is almost like peat to stuff that is more like fiber and other stuff is like chips so it would depend on what you got and if it is salty or not as to if you should have soaked it first. I don't know much about the expanded shale so don't know what the recommendation should be there.

The tanks under the pots, what does the water look like now?