Where did my nitrites go? (and other questions)

Let's see if we can figure some of this out... this is an interesting puzzle.

First of all, your water change and gravel cleaning shouldn't have done much damage to the biofilter (nitrosomas apparently aren't that important in FW tanks as we once believed, but that's a quibble...). The oxidizing bacteria attach firmly to surfaces and won't be dislodged by gravel vacuuming.

A couple possible things that may have happened: if you had a LOT of algae, it may have been scavenging ammonia and confusing your testing results a bit. Also, if you cleaned the tank walls well, you might have dislodged some of the beneficial bacteria.

That's not what I think is primarily responsible for the drop off of nitrite production, though. I suspect your pH has dropped sufficiently that the beneficial bacteria are slowing down or stopping their consumption of ammonia. I'm assuming your test only goes as low as pH of 6.0. If so, your pH could be considerably lower, and there's lots of evidence that lower pH values (e.g., 5) result in impairment/death of the beneficial bacteria.

Why the drop in pH from 7.6 to sub-6.0? You don't give us figures for carbonate hardness (KH), but I'd wager to guess that you have very low KH in your water. KH serves to buffer water, taking up acids in the water and thus maintaining the stability of the water's pH. A byproduct of the oxidization of ammonia/nitrite is acid (bioacidification); this acid is absorbed by the carbonates and bicarbonates in the water until they're saturated. At that point, the acids start to lower the pH. This sort of pH drop in low KH water is commonly seen in tanks that are cycling.

What can you do? Test the water (or ask your LFS to test it) to see what your KH is. If it is indeed low/nonexistent, you need to get add some buffering capacity to your water by way of increasing KH. You can add baking soda as a short term fix. My experience with baking soda is that it's hard to maintain stable KH (and by extension, pH) when using it, especially with water changes. I prefer adding some crushed coral to the tank. A bit in a nylon stocking, stuck in the filter should do the trick; start with a couple tablespoons and measure KH every several days over a couple weeks. KH should stabilze and you'll be able to see if you need to add or subtract some of the coral in the filter.

After the tank has cycled (i.e., you're getting zero ammonia/nitrites 24 hours after dosing with ammonia), you can remove the starter gravel. The bulk of the beneficial bacteria will inhabit the most preferential spots: this is generally in the filter and on the uppermost layer of gravel. As long as you don't remove the filter media or lots of the gravel, you should be OK.

I'm not an authority on plants, but from what I've read, it's generally best to hold off planting until the fishless cycle is through. Otherwise, as I understand it, there are likely to be significant algae problems.

Sorry for the long reply... I hope it's helpful.

Jim

Canucks - one thing I can't decipher from your original post is how much Ammonia you have been adding and when. Can you provide some info on that. Is it only those couple of instances you mentioned? Or ???

It doesn't mean much that your LFS doesn't recommend fishless cycling. LFSs are notorious for giving bad advice and recommending expensive products to 'cure' non-problems. Always take anything they say with a large grain of salt.

One thing I don't understand: you say your KH is -10 and your GH is -20 from the tap. I don't think you can have negative values for these -- the lowest is zero. Can you explain?

I'm surprised your addition of crushed shells had such a quick effect. It usually takes at least a few days to see much of a jump in KH. As for your target, I'd shoot for 80-100 ppm KH. That may bring your pH up a bit, but if it stays below 7.4 or 7.5, I wouldn't worry about it. If KH starts overshooting 100 ppm, you might want to remove some of the shells until you find the right amount to just keep KH at 100 ppm or so. You will want to leave them in there, because they work by dissolving slowly and replenishing any KH used up by normal acidifying process in the tank (like the oxidizing of ammonia & nitrites).

A caution: despite what your LFS may say, DON'T buy a product to mess with your pH. Even if you pH goes up (and the KH should drive it up a bit), you don't need to adjust pH. Trust me, it will just cause more problems if you start adding junk to control pH.

HTH,
Jim

Yes, to second what Jim says about your LFS and fishless cycling - just ignore them

I frequent 2 LFS - When I was checking out some fish while my new tanks cycled Iand they asked if I needed any help - I would explain I am just looking while my tank cycles. One thought I escaped from some asylum when I was telling them how I fishlessly cycled the tank - they just didn't believe/ understand the concept. The other, better store understood it but really didn't trust it or endorse it.

So stick with what you find here on fishless cycling - not at your LFS

Canucks - Ok, you are dosing your ammonia back up to 5ppm - correct? you are not adding 5ppm each day - right?

For your ammonia readings, when are you taking them - ie when you say you have a measurement of 2.4 ammonia, how many hours is that after you last added ammonia to get up to 5ppm?

the reason I ask is you can overdose with ammonia and inhibit the bacteria you need from growing quickly.

Plus for instance, the last 5 days - you are showing Ammonia at 2.4 (except for the last day at 1.2) and nitrite at .1
Thus, if you are dosing Ammonia back up to 5.0 ppm, how many hours are going by til you get that 2.4 reading?