New to the hobby - Unknown Molly Problem

[mollyman]

I'm new to the hobby and I'm having a problem with my mollies.

I have a 36 gallon bowfront tank with:

5 Mollies (3 silver female, 1 dalmation female, 1 black male)
6 Green tiger barbs
1 Oto cat
1 Incredibly Chill Clarkii Crayfish (seriously he wouldn't hurt a fly. We had feeder fish in with him in his original smaller tank and they survived for 4 monthes without so much as a threatening posture from him)

Water parameters are in perfect order and haven't changed since I cycled the tank.

No ammonia, no nitrites and no nitrates
Steady 7.0 PH
Light salinity (2 teaspoons of AQ salt in the whole tank)
kH at just over 40 ppm
gH at 30 ppm

I know the kH and gH are a little high but the water around here is already pretty high and I use sodium bicarbonate to adjust PH as the water is a tad acidic here too.

The tank is also lightly planted with 5 anubiases and a floating wad of hornwort.

Now for the actual problem. A little while ago (about a week), my mollies very suddenly got incredibly skittish with no discernable reason for it. They dart and hide, occasionally impacting with the side of the tank, at the slightest provocation. They all seem to have their frills up at all times. This is very strange behavior as they were very friendly prior.

Soon after, my barbs got skittish too, but I feel like that's a reaction to the mollies as they were fine for a few days after the mollies started being weird.

The only two inhabitants to exhibit normal behavior now are the Oto cat and the clarkii, both of which act as though nothing is wrong.

It bears mentioning that all 4 of my female mollies are pregnant and prior to this outbreak of strange behavior, two were becoming rather rectangular and were, I assume, ready to birth.

Curiously, I did a light water change recently and they briefly reverted to their old selves. They even let me touch them. The next day they were darting again however.

I am at a loss, and could use some help.

 

[Aiken Drum]

How long has the tank been set up?

What is your normal water change schedule?

Your water parameters are essentially impossible, unless you did the test following a near 100% water change. It suggests to me that there is something wrong with your testing, and the fact your water change improved things also says its a water quality issue.

Nitrate is the end product of the nitrogen cycle. In ordinary circumstances the only way to remove nitrate is changing the water. Change 50% of the water, remove 50% of the nitrate. The only way to get 0 nitrate in a cycled tank is if you are testing water after changing out all the water for water with no nitrate.

Its possible in a very heavily planted, low stocked tank that the plants take all the nitrate, but thats not the case from your description.

In a cycled tank you should see nitrate. In an uncycled tank you should see ammonia and/or nitrite depending on how far progressed your cycle is. Something isnt right with your testing.

 

[mollyman]

I don't know what to tell you Aikan.

I've been testing with the API master test kit and following the instructions to the letter.

I have been told from many planted aquarium enthusiasts that hornworts are nutrient sponges, however, and it could be possible that the hornwort is eating all the nitrate produced by the system.

The tank itself has been set up since last fall. Several months. I cycled it using ammonia solution over six weeks as per common instructions on the internet.

I do a 20% water change weekly. Occasionally, if I notice the water has become somewhat cloudy or that there's more shmutz than usual on the bottom, I'll increase that number.

I'll do a fresh round of testing on the water using my API kit when I get home from the gym and post results.

 

[Aiken Drum]

Really bang bottle #2 of the nitrate test on the counter. Shake the heck out of it.

 

[mollyman]

alright im back with new parameters

It was a bit of a shock to be honest.

PH 7.4 (yikes, not what they're used to)

Nitrate ~5-7 ppm

Ammonia 0 ppm
Nitrite 0 ppm

I'm going to do a small water change now to bring down the PH.

 

[mollyman]

Small update,

I adjusted the ph down to ~7.1 and in the process, discovered that one of my mollies had given birth to three healthy fry.

I fully expect them to be eaten by the other tank inhabitants, which suits me fine, but more importantly, mollies can cancel their labour if they're too stressed.

I think I misconstrued normal skittish pregnant molly behaviour for problem behaviour. I have heard tell of pregnant mollies causing a ruckus in tanks before, and I have 4 of them.

Thanks very much Aiken for your help!

 

[gilpi]

My advice, don't get too fixated on testing the water, stay away from adding salt or anything else to your tank other than water conditioner when changing/adding fresh water to the tank and "adjusting" ph, highly NOT recommended. What is recommended is lots of partial water changes. Funny you mention most of your fish darting around after the mollies did, I had a similar incident with my tiger barbs, I added some tetras in the tank that were skittish for about a week, all of my barbs started acting the same way till the tetras adjusted to the tank a week later.