Low pH, low KH, High GH

[maxthedog123]

I have a situation I am trying to understand. I was testing water yesterday and ran the API test for pH. I don't typically test for that, but I was puzzled that the pH showed up as 6.4. As a side note, I believe my tap water is around 7.2.

This is my 55g tank that has been set up for probably 3 years.

Current stocking: 4 angels (~2in each), 5 denisonii barbs (~1.5in each), 2 columbian tetras, 4 scissortail tetras (m. intermedia NOT rasbora), 1 SAE and 1 BN pleco. Lots of plants in this tank: vals, java fern, banana plant, wisteria, 1 large sword, 2 small swords. I do have mopani wood in the tank, but I haven't seen any noticeable tannins in quite some time.

To be honest, my maintenance has been a bit suspect lately. (I know, but sometimes life gets in the way.) I've been changing the water about once every 2 months. I know there will be disagreement on that, but I have been going lower and lower tech for some time now. I have 2 aquariums that are pure Walstad setups. My 55g and 30g now have low light, tons of plants, no CO2 and light fertilizer maybe 1x per week. Reading Tom Barr's sticky on this site about water changes causing fluctuation in CO2 levels, I have been shooting for less variation in CO2 levels. My understanding is for a lower tech setup, changing CO2 being a bad thing for algae control.

My nitrates seem stuck at about 40. After a water change today, the results were as follows: pH 6.6, ammonia 0, nitrite 0, nitrate 40. I tested GH and KH for the first time in a long time. KH was either 1 or 2 - it was hard to read, but no higher than 2. GH was around 20. Just for fun, I tested the tap water: KH was 4 and GH was around 20. (Lots of limestone here in Southwest Ohio.)

I also cleaned the Fluval 405 which hadn't been cleaned in about 6 months, so that may make a difference too. I have a 305 on the tank as well - I need clean that. Is it better to wait to clean it or is it more imperative to get the dissolved organic gunk/sludge out of the system?

The plants grow well - my Vals are at the top of the tank and my sword puts out new leaves on a very regular basis. Wisteria is booming. The only thing that doesn't seem to get very large are the crypts, but they may just be getting muscled out for the nutrients.

Just for a complete picture, I switched from T5HO lights (108w) to T5NO (~56w) several months ago. I quit running CO2 at least a year ago. (Dialing down the lights got the BBA in check.) I use the Seachem liquids around 1x per week. Will be moving to dry ferts when the 2g jugs of that I have are gone.

I don't think based on the current size of the fish that I am particularly heavy on fish load. Everyone has been fairly healthy except for 1 angel who developed pop eye and started to have some erosion on one of it's gills. I treated the tank with Marycn2 (sorry, QT is not up and running). I had to put the angel down. I've given everyone else a very close inspection over the last 2 weeks and I have not seen any other signs of health issues.

So, I will test later to see if pH moves at all. Do I need to do something to buffer the water?

I am going to self diagnose and then ask for your thoughts. I am going with the cause of low pH due to excess nitrate buildup in the canister filters. (Somewhat of an "old tank syndrome".) From what I have read, breaking down nitrates and/or excessive decomposing organic material will cause a drop in pH as well as a potential drop in KH due to acids being produced.

Opinions? Just more slow maintenance (to avoid a crash or just plain killing the fish through shock) or do I also need to consider a KH buffer? It seems like my KH is rather low and I could benefit from buffering. What is the best method to buffer KH? Old fashioned baking soda? A specialized buffering product? Other remedies or do I just need to leave it alone?

 

[maxthedog123]

Today's update: I did a 20% water change again today. pH has crept up to 6.8 and KH was a solid 2. In other words, when I did the API test a couple of days ago, I was pretty sure the test turned a pale yellow on the first drop. Today I got a definite blue on 1 and yellow on 2.

Ammonia is 0 and nitrite is 0, but nitrate remains a solid 40 on the test. 4-5 days ago, I was unsure if I was reading 40 or 80 (the next mark on the test) because the red didn't quite match either one. Why the stubborn nitrate value?

I still haven't cleaned the second canister filter. As I mentioned, I cleaned the larger 405 yesterday. I was pretty careful to keep everything in tank water. I did replace the (rather disgusting) floss in one tray with new bio balls, but I doubt that will have any effect on the bacteria in that filter. Do I clean the second one now or wait to make sure I don't start a cycle? I know my 305 is full of black sludge just like the 405 was.

 

[Cyclesafe]

Your nitrate test kit may be suspect. Calibrate it using the method posted elsewhere in the Barr Report. Alternatively, use half of the sample amount called for in your test and top off (to 5ml?) with distilled water. Run the test again to see if your test kit registers the lower concentration. My bet is that your kit is the problem.

I always clean out both of my filters at the same time on the theory that my planted tank is fully capable of oxidizing fish-excreted ammonia even without them.

 

[maxthedog123]

I actually had that thought about the test kit. I bought the kit in 2007 and it had 06 manufacture dates on the bottles, so I bought a completely new test kit yesterday. Whatever the old one was, I have to think the new one is accurate at 40ppm. Unless it's totally bad?

I've been busy today, but I am leaning towards getting the black gunk festival of nitrates out of the 305 sooner rather than later.

 

[Cyclesafe]

Just because a test kit is new is not a sufficient reason to take action based on its results. Calibrating each time it's used is the only way to ensure that it is accurate. Having said that, however, for a planted tank, 40 ppm NO3 could even be desireable. As I suggested above, test the kit at half the concentration of aquarium water and see if your kit shows half the amount of nitrate. If so, then you can conclude that the kit is at least distinguishing varying concentrations even if you haven't yet verified its accuracy.