Stocking? I'm In Such A Mess!

[nofishinginmytank]

I have been doing everything by the book. I have been following everyone's advice. 3/2 years ago I bought my first tank and completed the fish less cycle before adding any fish. I have had such terrible bad luck and have experienced quite a few deaths but after doing a lot of research I have avoided adding any fish at all for the past 10-6 months and we hadn't had a single death until last week. Our tap water pH went down to 5.9 and killed half of my fish after they had been cleaned. After testing the water we found the problem and have since used a pH water treatment to fix it and everything has been going well since. But I am now in a horrible mess with my stocking. 
My tank is the marina 35 litre tank. W50xD25xH30cm. I have the interpet PF mini filter and the marina heater which is reccomend for the tank.
I currently have:
3 female platies
1 male swordtail
1 male dwarf gourami
 
I understand that the stocking is far from ideal but it's what I am left with. I just want to know what I should do really? Thanks, any advice will be much appreciated.

 

[Byron]

This is a 35 litre tank (= 10 gallons) so keep in mind that from the fish's perspective this is a small space.  But the first issue is the water parameters.
 
The platies and swordtail are harder water fish, whereas the gourami is softer water.  The gourami has some adaptability to slightly harder water, but the livebearers must have moderately hard water with a basic pH (basic means above 7.0, below 7.0 is acidic).  If the pH went down to 5.9, the platies and swordtail would have real problems.  But this is just pH, there is still the even more important GH which is linked.
 
So the first thing is to ascertain the GH of your tap water.  This is the general hardness, meaning the level of dissolved mineral in the water.  Connected to this is the KH, or carbonate hardness (sometimes termed Alkalinity).  This buffers the pH, preventing fluctuations to some degree.  These numbers you should be able to get from your municipal water authority; check if they have a website, as water data may be posted.  Or you can ask them directly.
 
Once we have the GH and KH, it will be easier to predict what the pH may do.  And on this, the best way to adjust the pH is not with chemicals but with some natural methods.  I won't get into this until we have the numbers.  But I will say that if the GH/KH turn out to be on the soft side, the pH will tend to lower naturally.  And the livebearers will not last long, or if they manage (depending upon the numbers) they will not be in the best of health.
 
Once we have the GH/KH it will be easier to decide on fish.  But at this point, I must mention that a 35 litre tank is not going to provide adequate space for the swordtail (this fish can reach 6 inches (15 cm), though in aquaria it is normal to attain 4-5 inches (10-13 cm).  Platy is not quite so large, at 2-3 inches (5-8 cm).
 
Byron.

 

[Brodeur30]

I've never seen a swordtail reach 3 inches, but there are several varieties. That tank is pretty full just from the gourami alone. Once your water situation is taken care of you could probably add a small algae eater or bottom feeder

 

[nofishinginmytank]

Ok, thank you both. I am currently contacting my water supplier to find out my water parameters and I'm also treating my water to get my pH to a safe level again. 
Thank you for your help and advice

 

[Byron]

Ok, thank you both. I am currently contacting my water supplier to find out my water parameters and I'm also treating my water to get my pH to a safe level again. 
Thank you for your help and advice

 
I would not recommend treating water to adjust the pH, it won't likely work, plus these chemicals are hazardous to fish.
 
I'll offer some further explanation now, to help you understand this rationale.  The pH is connected to the GH and KH.  In every aquarium, the pH will tend to lower naturally over time, due to the continual acidification caused by bacterial processes in the substrate primarily but also the filter and elsewhere.  The extent to which the pH lowers depends upon primarily the GH and KH of the water, and then the fish load.  Trying to interfere with this natural process usually will not work, unless it is done "naturally."  For example, if your GH and KH are very low, as I would suspect, then you have no natural buffer to prevent the pH from falling.  If the water is higher in GH and KH, the buffering capacity increases proportionally, and may prevent the pH from lowering.
 
If you do have very soft water, and want to keep livebearers, then the GH and KH must be raised, and the pH will naturally rise accordingly.  The only safe way to do this is with calcareous substances, either in the substrate or in the filter.  Rock that is calcareous, meaning it is composed of minerals like calcium and magnesium, will slowly dissolve minerals into the water.  Limestone, marble, dolomite, aragonite, crushed coral, shells are all calcareous, so a substrate gravel or sand made from such rock will work, or for less of an increase, a quantity of such sand can be placed in the filter in a nylon mesh bag.  However, the GH/KH and pH can rise very sharply doing this, so it mujst be thought out and controlled.  We need to know the GH and KH before considering this.
 
As for chemicals that allegedly adjust or somehow manipulate the pH, these are not really safe.  First, they can cause a sudden change which then suddenly ends when the natural biology takes over again, and a fluctuating pH is highly dangerous to all fish.  Second, even if they work, or seem to, they are chemicals in the water and thus they get inside the fish.  This is not good for any fish, and some will have serious issues leading to sickness and even death.
 
I will be happy to answer any questions you may have, once we know the numbers.
 
Byron.

 

[nofishinginmytank]

I am taking my water to be tested again tomorrow and the water company have said that they will email me the figures. I have been sold these little pH crystals that you dissolve in warm water before adding it to the water. Do you think these will work?

 

[Byron]

I am taking my water to be tested again tomorrow and the water company have said that they will email me the figures. I have been sold these little pH crystals that you dissolve in warm water before adding it to the water. Do you think these will work?

 
Probably not, at least not permanently.  But we are guessing a bit, until we know the GH and KH, as they directly impact the pH.  I am assuming your water is very soft, and this means the pH will continue to lower, no matter how many times you raise it with chemicals, and this is bad for all fish.

 

[nofishinginmytank]

Yes, I have been told that our water is quite soft. Is there anything I can do?

 

[Byron]

Yes, I have been told that our water is quite soft. Is there anything I can do?

 
I answered this back in post #5--but I cannot stress too much that we really need to know the actual GH and KH before we consider options.